What is the heart, according to the Bible?

In Scripture the heart is the centre of the thoughts, the affections and the will (Matt. 9:4; 12:34; 24:48), that is, the inner “switchboard” of man. This is why the writer of the Proverbs had already said, “Keep thy heart more than anything that is guarded; for out of it are the issues of life” (Prov. 4:23). This is an important warning!

The heart is often referred to in scripture as the seat of the affections and of the passions, also of wisdom and understanding — hence we read of 'the wise in heart,' also the Lord gave to Solomon 'a wise and understanding heart.' It is the centre of a man's being. But before the deluge God's verdict of man was that every imagination of the thoughts of his heart was only evil continually. Gen. 6:5. A similar verdict is found in Gen. 8:21, after Noah came out of the ark. And the Lord said, Out of the heart of man proceed evil thoughts and every form of wickedness. Mark 7:21. The law required man to love God with all his heart. The reception of the gospel must be in the heart, Rom. 10:9; and God enables a hearer to receive the good news in 'an honest and good heart,' upon which there is fruit. Luke 8:15. In new creation there is a 'pure heart,' the Christian being led by the Holy Spirit. 1 Tim. 1:5; 2 Tim. 2:22; 1 Peter 1:22.

For scripture uniformly teaches that the heart is the core of man's being. It is the seat of the affections and of the impulses that carry man forward in the path of life. The Lord Himself declared to those who were content to make clean the exterior of the platter that there is a fountain of uncleanness within, which they entirely ignored. It is from the heart that proceeds every thing that defileth (Matt. 15:19). The evil heart of the natural man therefore gives a colour to his every action; for it is thence the mischief springs (Matt. 5:28, 1 John 3:15). On the other hand, the heart of the renewed man is so to characterise every action that it may prove good and acceptable before God. As servants of Christ we are to do "the will of God from the heart" (Eph. 6:6). To this end the love of God has been "shed abroad in our hearts by the Holy Ghost which is given unto us" (Rom. 5:5). Indeed the very Spirit of God Himself is in our hearts to originate and characterise every affection. This the apostle teaches, "Because ye are sons, God hath sent forth the Spirit of His Son into your hearts, crying, Abba, Father" (Gal. 4:6; 2 Cor. 1:22).

This fact is of great moment to such as have learnt the deceitfulness of the natural heart (Jer. 17:9). We are not left to ourselves to produce proper feelings Godward. He Who gives us right thoughts of God and the Father gives us right feelings too. For He is the Spirit of love as well as of a sound mind (2 Tim. 1:7). It is He, Who fills the heart with such a sense of the incomparable love of God Rom. 5:5) that out of the abundance of the heart the mouth speaks (Matt. 12:34-35; Luke 6:45).

Our subject is thoughts themselves and though we shall necessarily have much to say about the mind as the thinking organ, we must not forget that the ultimate control lies deeper still. “Out of the heart of men proceed evil thoughts. …” (Mark 7:21) said the Lord Jesus. The word of God is “a discerner of the thoughts and intents of the heart.” (Heb. 4:12)

But as the “heart” of man is the spring of evil, so it is the channel for good; and when cleansed of God it is where “Christ may dwell.” “Out of its abundance,” for good or evil, it “speaks.” “With the heart man believes unto righteousness;” it is “purified by faith”; the “pure in heart see God.” It “cleaves with purpose of heart to the Lord.” God’s love is shed abroad in it. It is a good thing that it be established in grace. When God said, “Seek ye my face,” my heart said, “Thy face Lord will I seek.” God would say too, “My son give me thine heart.”

These words, quoted from Luke 12:45, are those of the evil servant, and are said “in his heart.” These inaudible heart expressions had not assumed an articulate form in such a way that others could hear them. They were none the less real, for, after all, the heart is the seat of affection and desire; and in that sense, when the desires are active, it commands the tongue. It is “out of the heart that the mouth speaketh.” Even supposing that no actual language be used, conduct corresponding to the desires of the heart will be displayed. Hence we need to “keep the heart with all diligence, for out of it are the issues of life.” We long for the gratification of our hearts’ desires; we labour for them.

But it all began with the heart. There is no doubt that the heart controls the man. The mind may tell you that such and such a course is not right, but it is the heart that carries the man.

As we have noted, the heart is the center of all motives and activities. Little wonder then that we are admonished, "Keep your heart with all diligence, for out of it spring the issues of life." Keeping the heart certainly involves carefully controlling the heart's desires, that it is not allowed to lead in devious ways. It produces "the issues of life" (v. 23), whether good or bad. But the person is given the responsibility of governing his heart. We all know this, though we may pay little attention to it.

Truth is moral as well as intellectual; and seeing that we are made of heart as much as of head—the heart having far more influence over us than the brain—it is necessary to own this effect of the Word on our ways. The heart is king, and the other members are its vassals. The will is liege-lord, and ever claims the throne.

The third and last section of the psalm is a prayer to God Himself, into whose presence the soul has thus been brought, to find itself naked and open to Eyes that see beyond all that the fullest self-consciousness can be aware of. And these inaccessible depths, what are they? What may appear in them, when the secrets of all hearts shall be exposed? Alas, it is not because of their profundity, but because of their tortuous labyrinths comes the difficulty — the impossibility — of exploration: "the heart is deceitful above all things … who can know it?"