Habakkuk 3:6 He stood, and measured the earth: he beheld, and drove asunder the nations; and the everlasting mountains were scattered, the perpetual hills did bow: his ways are everlasting.
Here is Habakkuk the prophet of old shows that God’s ways are everlasting. So not only is God everylasing, but his ways are everlasting. If God changed then He would not be everlasting, but he would become something new and so he would not really be everlasting, but a new thing that started at a certain point in time, but He does not change and even His ways are everlasting.
James 1:17 Every good gift and every perfect gift is from above, and cometh down from the Father of lights, with whom is no variableness, neither shadow of turning.
Jesus also never Changes. Jesus is one with God and was with God from the very beginning.
Matthew 5:17-20 17 Think not that I am come to destroy the law, or the prophets: I am not come to destroy, but to fulfil.
18 For verily I say unto you, Till heaven and earth pass, one jot or one tittle shall in no wise pass from the law, till all be fulfilled.
19 Whosoever therefore shall break one of these least commandments, and shall teach men so, he shall be called the least in the kingdom of heaven: but whosoever shall do and teach them, the same shall be called great in the kingdom of heaven.
20 For I say unto you, That except your righteousness shall exceed the righteousness of the scribes and Pharisees, ye shall in no case enter into the kingdom of heaven.
This is what is meant by Paul in {Romans 6: 14-15} when he says we are no longer under the law. That is because just as in the case of the law abiding police officer, those who walk in faith are above the law. That is because they walk in the Spirit and not in the flesh. The walk in the Spirit of the Law as Paul mentions in {2Corinthians 3:6}