"In Malachi 3.6 it says God doesn't change, that God is always the same. And yet in a number of places we read that God's mind was changed or that God repented about this or that. If God doesn't change, how can he change his mind?"
The Malachi passage reads, "For I the Lord do not change; therefore you, O children of Jacob, have not perished" (Malachi 3.6). In this verse's fuller context clearly God is telling the Israelites they need to be just and merciful or else. . . . However, the "or else" isn't annihilation, for that would break the covenant God had made with the nation. Instead, there is a threat of divine punishment. When we read the whole of the Old Testament, God reacts to Israel's sins time and time again with retribution bringing them close to annihilation, but always God relents from destroying them completely. So for Malachi God is unchangeable because, even though God demands holiness (that's never changed), God will not destroy the Israelites because of the covenants; therefore, God is unchanging.
And yet, many times in the Old Testament we read of God saying such and such shall transpire, but later "repents." For instance, God repents or is sorry for creating humanity in Genesis 6.6-7. In Jonah 3.10 God's mind is changed about destroying Nineveh, even though God had declared the city would be overthrown (Jon. 3.4). And in 1st Samuel 15.35 we read that God is sorry for making Saul king and so chooses another to replace him.
Further, there is a notion that God's mind can be changed. Abraham bargains with God over the destruction of Sodom and Gomorrah in Genesis 18. And in Joel 2.14 and Jonah 3.9 we see a call to righteousness to appease God and keep divine wrath at bay.
And then there's the New Testament. It seems God does a 180ø there becoming a "loving God" instead of the wrathful God of the Old Testament. Some claim it's the advent of Jesus Christ that makes the change, and yet if Jesus=God . . . did God change?
The answer to the question of whether God changes is dependent on one's understanding of the question. If to change one's mind means to change ones nature, then God clearly does change. However, God's nature doesn't seem to be dependent on the choices God makes. According to John Wesley our understanding of God comes from four sources: scripture, reason, tradition, and experience. In the Judeo-Christian tradition the use of scripture is the primary source for understanding of God. However, those writing scripture had only tradition, reason, and experience to rely upon. Certainly God was involved through inspiration and revelation, but the writer's understanding about God came primarily through what they'd experienced and what they'd learned in their tradition. In a society in which all natural phenomenon was attributed to the blessing or cursing of God it is hardly surprising that Old Testament scripture pictures a God who is generally angry with the world. Indeed, if today we had a similar understanding of God we too would conclude that God had it in for us just read the headlines of the world disasters, let alone community tragedies. If these were all attributed to God what other conclusion could we make?
But even in the Old Testament we see a different sort of God beneath the veneer of attributed anger. In Genesis 2 we see a God on hands and knees lovingly creating a human from the earth. In the psalms we read of the delight God takes in the faithful (Psalms 36.8; 37.23). And we see a God who shows concern for the welfare of even animals (Jonah 4.11).
In the New Testament there was a clear and different understanding about evil. God was no longer viewed as the sole provider of tragedy. The Israelites had come to understand that Satan was the father of lies and brought much evil into the world. And Jesus seemed to indicate that some disasters occur just because . . . (Luke 13.1-4).
In the New Testament there is an emphasis that God is a loving God. Indeed, in 1st John 4.8 the author states specifically that God is love. But the concept of a loving God is certainly not new to the New Testament. Many passages in the Old Testament refer to God as a loving and compassionate God (Exodus 34.6; 1 Kings 8.23; 2 Chronicles 6.14).
So, does God change? Although clearly God does have a change of mind occasionally, the very essence of God, the God who is manifest love, seems to be the same yesterday, today, and always (Hebrews 13.8).