Why is God so different in the Old Testament than He is in the New Testament?
The short answer is: He isn't. What changed is not God's character but the degree of His self-revelation and the principle on which He deals with people. The God who thundered at Sinai is the same God who embraced the prodigal son — and both the thunder and the embrace flow from the same holiness and the same love.
God Does Not Change — His Revelation Unfolds
The perception of two different Gods collapses once you see what Scripture itself says about how God makes Himself known. He did not change between Malachi and Matthew — He unveiled more of Himself.
F. B. Hole traces this unfolding:
F. B. HoleThe full revelation of God, however, awaited the coming of the Lord Jesus. The utmost that was possible even for so great a man as Moses was to see "the back parts" of Jehovah (Ex. 33:23). Certain of the divine attributes were emphasized such as His mercy and long-suffering; the full-orbed revelation of Himself was only possible in the only-begotten Son who was God and became Man. "No man has seen God at any time; the only-begotten Son, which is in the bosom of the Father, He has declared Him" (John 1:18).
The Old Testament was not a lesser revelation from a lesser God. A. J. Pollock makes this emphatic:
A. J. PollockIt is not that the Old Testament is not as fully inspired of God as the New. The Old is of EQUAL INSPIRATION AND AUTHORITY with the New, but God has been pleased to make a fuller revelation on these subjects in the New. It is emphatically not a question of evolution but of revelation.
And Samuel Ridout shows that the apparent "progress" in doctrine was not God learning as He went, but deliberately pacing what He disclosed:
Samuel RidoutI have been speaking of what runs through the Book as a whole — one steady, consistent onward movement. Casual readers may notice what has been called "the progress of doctrine," but the devout student will be more and more impressed with the perfect knowledge from the beginning of the Divine Author, withholding full statements till their proper place, but giving from the beginning intimations and glimpses of what was before Him at all times.
Same Holiness, Different Method
The real contrast between the testaments is not between an angry God and a loving God — it is between law and grace as two different methods the same God uses to accomplish the same goal: making His people holy.
C. H. Mackintosh states this with great clarity:
C. H. MackintoshThere can be no alteration in this. Dispensations may change, but God, blessed be His name, can never cease to be "the holy, holy, holy Lord God of Israel;" nor can He ever cease in His effort to make His people like what He is Himself. Whether He speak from amid the thunders of Mount Sinai, or in all the gentleness and grace of the blood-sprinkled mercy-seat in the heavens, His object is still the same, — viz., to make and keep His people holy.
F. B. Hole captures the contrast in a memorable formula:
F. B. HoleUnder law God, so to speak, stands before us saying, "Give! render to Me your love and dutiful obedience." Under grace He stands with full hand outstretched, saying, "Take! receive of My love and saving power." Law says, "Do and live," grace says, "Live and do."
The law was never meant to be the final word. It was, as Hole explains, a provisional arrangement — a schoolmaster "up to Christ." When Christ came, the believer was brought from the position of a child under age into "the full liberty of the Father's house."
Goodness and Severity in Both Testaments
People sometimes speak as if the Old Testament is all wrath and the New Testament all love. But both qualities run through both testaments. And God's tender mercy shines throughout the Old Testament law itself.
Mackintosh illustrates this beautifully from Deuteronomy 19, where the same passage that speaks of God cutting off the nations of Canaan also provides cities of refuge for the manslayer:
MackintoshThere is peculiar sweetness in the expression, "Thou shalt prepare thee a way." How like our own ever gracious God — "The God and Father of our Lord Jesus Christ!" And yet it was the same God that cut off the nations of Canaan in righteous judgement, who thus made such gracious provision for the manslayer. "Behold, the goodness and severity of God."
The Cross: Where Justice and Love Meet
If anything, the New Testament presents a more solemn picture of God's holiness than the Old. Mackintosh presses this point home when comparing the law's treatment of a rebellious son (stoning, Deut. 21) with the father's embrace of the prodigal (Luke 15):
The law said, "Lay hold on him" — the Gospel said, "Embrace him;" the law said, "Stone him" — the Gospel said, "Kiss him;" and yet, be it remembered, we meet the same God in both. The God of Israel speaks both in Deuteronomy and in Luke.
And the Cross is where it all comes together:
LAWGRACEAll the stones that were ever cast at offending sinners — all the penalties that were ever inflicted — yea, we shall proceed further, and say, that the eternal punishment of the wicked in the lake of fire, could not afford such a solemn proof of God's hatred of sin, as the scene on the cross. There it was that men and angels might behold God's thoughts of sin, and God's thoughts of sinners. His hatred of the former, and His love for the latter.
J. N. Darby adds a further dimension — even in the Old Testament, pure law was never the whole picture. God always mingled mercy with it. But what was needed was a full, unmingled revelation of grace:
J. N. DarbyGrace has this character; it is not simply love (it is perfectly love, but it is not simply love); it is love acting where evil already is, and towards that which is evil. There is perfect love between the Father and the Son, but that is not grace. Grace is the exercise of this same perfect holy love towards that which is totally unworthy of it.
The God of the Old Testament is not a different God from the God of the New. He is the same holy, loving, unchanging God who was progressively making Himself known. In the Old Testament He revealed His power, His faithfulness, His righteous demands. In the New Testament, in the person of His Son, He unveiled the fullness of what He had always been. The law showed what God required; the gospel shows what God provides. The severity was always accompanied by goodness; the grace was always grounded in holiness. And the Cross of Christ is the place where it all comes together — where the most terrible display of God's hatred of sin is, at the same moment, the most glorious display of His love for sinners.