What does the Bible say about ingratitude/unthankfulness?

Nor should we overlook the next pair of humiliating characters in these last days: "unthankful, unholy". These appear to be as appropriately set together as their two predecessors were, and indeed all those described hitherto: not that those who read them unconnectedly do not glean instruction from each and all, but that the observance of them jointly gives order, and adds to the harvest. Now what an anomaly is a professing Christian who is thankless! He professes to have life in Christ, and the forgiveness of sins; he is baptized to Christ's death whereby he died with Him to sin; he is under grace, not under law, that sin should not have dominion over him; he is in Christ and so freed from condemnation, and has received the Spirit of adoption whereby to cry Abba, Father. For if any man has not the Spirit of Christ, he is none of His. All this individually belongs to the believer. Think next of the precious privileges he enjoys as being of the body of Christ, in the worship, in the apostolic doctrine, in the fellowship, in the breaking of bread, in the prayers; not to speak of that holy and wholesome and most needful discipline which attaches inseparably to those who keep the feast on the sacrifice of Christ. But why need one set out these countless blessings which all saints share in His Name and by the Spirit of our God with which scripture teems? To be "unthankful" then, while bearing that Name which ensures all to the believer, is the extreme of ingratitude.

So also when the tax-gatherers came to be baptized, instead of dismissing them contemptuously as a mere Jew would have done, he answers their question, "Master what should we do? And he said to them, Take no more [money] than what is appointed to you." Notoriously they were extortioners, their rapacity was proverbial; they plundered the people of whom they were the official tax-gatherers. The soldiers similarly "asked him, saying, And we, what should we do? And he said to them, Oppress no one, nor accuse falsely; and be content with your pay."74a It is clear that here we are warned against violence and corruption, the two great features of men left to themselves. But, besides, contentedness with their pay is pressed upon them. It is remarkable how much the spirit of contentment has to do not only with the happiness of a soul but with its holiness. There is scarcely another thing that so tends to disturb our relationship with God and man as discontent. It makes an individual ripe for any evil. It helps, on a great scale, to the revolutions of nations and other social ruptures. On a smaller scale, it subverts the equilibrium of families and the right attitude of individuals as nothing else can. So we read of "unthankful, unholy" classed together by the Spirit of God. We also find unthankfulness mentioned as leading into idolatry. The Gentiles not only did not glorify God as God, but they were unthankful, and they fell into all kinds of moral depravity. There is nothing more important than to cherish a thankfulness of heart, sanctifying the Lord God in our hearts, having confidence in His goodness, and also in the certainty that He has given to ourselves individually exactly the thing that is best for us. But the only way to be thus content, whatever may be our lot, is to look at God as dealing with us in Christ for eternity.

(7) “Unthankful” or “ungrateful”. By those who are disobedient to parents, every mercy from God or men is received as a matter of right wherein there is no call for gratitude. Christianity teaches us that all creature mercies are “to be received with thanksgiving of them which believe and know the truth” (1 Timothy 4:3).

(8) “Unholy” or “profane”. If ungrateful for blessings temporal and spiritual, men will soon scorn and despise the mercy and grace that bestow the blessings. Esau profanely despised the birthright by which God would have blessed him.

I suppose this is the reason why the Son is designated “The Word.” The word is that by which God makes Himself manifest, it is the means by which He gives expression to His mind and will. Creation brought to light His power and divinity, and this was the work of the Son, who is not only God but the Word of God. We read in the beginning of the gospel of John, “In the beginning was the word, and the word was with God, and the word was God. The same was in the beginning with God All things were made by Him, and without Him was not anything made that was made.” The heavens and the earth, as I have been saying, brought to light His power and divinity; but this was not all that could be brought to light, there was still His nature to be made known. But the ray of light that men possessed was very quickly given up. They did not like to retain God in their knowledge; He was not the kind of being that their hearts desired; they would have preferred a god with passions like their own. They had known the true God, but they glorified Him not as God neither were thankful. It is a great favour bestowed upon the creature, to be given a little light as to the blessed God. It is that which lifts man above the level of the beast. And how thankful the creature should be for that light! Where the light is appreciated thanks will be given to God for it, and where no thanks is rendered to Him it is a sure sign that the light is despised, and will soon be given up. “Neither were thankful.” What a dreadful condition of mind and heart. But it only shows that from the beginning man desired not the knowledge of God. The language of the heart of man from the moment that sin entered the world has been, “Depart from us, for we desire not the knowledge of thy ways” (Job 21:14).

His brother replied to the effect that not all the money in the world could purchase a single grain of wheat, unless God had created it, giving it the power to reproduce itself, and then to sustain human life when used as food. He created the sun which ripens the grain, and gave water, as rain, to bring it to maturity. This, and more, showed how hopelessly shallow his unthankful spirit was. Alas! countless multitudes are unthankful. Scripture warns us that one of the signs of the last days is that of men being “unthankful, unholy” (2 Tim. 3:2).

The men of this age are peculiarly marked by unthankfulness — see, 2 Timothy 3:2. They see the hand of God in nothing, and if perchance things go well with them they only say "My luck was in." It is our privilege to see the hand of God in all things, and, walking in His fear, to trace His ways with us in a thankful spirit.

The next ground is not the knowable but the positively known. "Because, having known God, they glorified him not as God, nor were thankful, but became vain in their reasonings, and their unintelligent heart was darkened. Professing to be wise, they became fools, and changed the glory of the incorruptible God into a likeness of an image† of corruptible man and birds and quadrupeds and reptiles." (Ver. 21-23.) A traditional knowledge of God is in question; and as the former regarded man with evidence from the beginning calculated and adequate to indicate a divine First Cause, so the objective knowledge of God here spoken of was the portion of man even after the flood: indeed not till after that mighty event do we hear of idolatry. But man was unequal to the task of preserving the holy deposit; and this, because of his moral state. When they did know God, they neither glorified Him as such, nor were they thankful. This left room for vain reasonings, which again darkened the heart instead of leading it into light. It was the self-sufficiency, and so the folly, of the creature. For light is only seen in God's light, and man must sink into darkness when not morally elevated by looking up to One above him. The humbling proof appeared too soon; and philosophy but sealed the evil to which superstitious fear led the way. An unacknowledged Supreme was rapidly forgotten, and the glory of the incorruptible God exchanged for a likeness of an image of corruptible man, yea, into objects ever lowering till creation's lords, now the victims of this debasing delusion, worship the most loathsome reptile which eats the dust.

In the creation the Gentiles “knew God.” This is indeed not the conscious, vital knowledge derived only from new birth, but the distinct evidential knowledge that renders their guilt inexcusable. They wilfully refused to give God His own place: no pulsebeat of thankfulness would they have toward Him. They would receive His blessings, cut off the very hand that gave them, and proceed to pervert them to the full. The inward reasonings of their minds, because bent on following their own wills, dragged them into folly; and their hearts, wilfully without understanding, were colored by the darkness they chose. Moreover, the very reasonings that led them to such darkness they professed to be wisdom! — a profession which the more thoroughly declared them fools. This was their development — or evolution, if you will — “they became fools.”

How marked is the contrast between that little company and the Gentile world in Paul's day! Barbarism, savageness, ignorance of God — these with their attendant evils, rife at the date of our epistle, were not characteristics of those who emerged from the ark. Man, not God, was responsible for the condition of the Gentiles. God had provided a perpetual witness in the work of creation, and within the cognisance of all, to His eternal power and Godhead. That which may be known of God had been manifested to His creatures. Of this the psalmist sung in days of yore (Ps. 19:1-6) pointing us to the heavenly bodies, whose forms and whose movements, unalterable by man, have a voice for all, since their line has gone out through all the earth, and their words to the end of the world. Thus there was that which was known of God. Besides this, Noah and his sons had worshipped Him. God too had blessed them, and had spoken to them (Gen. 9:1-17). But He who is, and ever must be, the proper object for the creature's heart, ceased through the creature's wilfulness, and who can say how soon, to have His right place in that heart. Men "glorified Him not as God, neither were thankful; but became vain in their imaginations (or, reasonings), and their foolish heart was darkened" (Rom. 1:21). Before the flood, man's will was at work — corruption characterised the race (Gen. 6:12). After the flood, the mind worked. They became vain in their reasonings. They turned from the light. So their senseless hearts became darkened. Darkened. Let us mark the term — not dark. It speaks not of a primary state, but of one induced, and that by man. He was not created in that condition. He had not to grope his way out of a primeval moral chaos, with darkness all around, into the light such as is afforded us by revelation, and understanding about God. Nor was any one of that little company surrounding Noah's altar darkened in their understanding. In time man's foolish heart, we learn, became darkened, as he turned away from the only source of light and true knowledge which had once been possessed. Then priding himself on wisdom he became a fool, and idolatry was the result (1:22-23). The downward road is clearly traced. They "changed the glory of the uncorruptible God into an image made like to corruptible man, and to birds, and four-footed beasts, and creeping things." They became fools. They changed the glory of God. How low did they sink, when they worshipped creeping things! How foolish to worship that which God had originally made subject to Adam!

Neither glorifying God in His works, nor thanking God for His temporal mercies, they lost the knowledge of God that they possessed. Refusing the witness of Creation, they fell back, as men are doing to-day, upon their own imaginations. Thus their foolish heart was darkened, that is, they lost the knowledge of God. Moral darkness is always, in Scripture, ignorance of God; even as light is the knowledge of God. The more foolish they became the more they professed to be wise: and the more they professed to be wise the bigger fools they became.