So many people argue that over the course of time God has changed in His nature.  They claim that the character of God seen as angry and "cruel" in the Old Testament is far removed from the loving, merciful, and "permissive" God of the New Testament.  Let me suggest an answer to this question and then back it up with Scripture.  I contend and the Scriptures support that the nature of God has not changed as Malachi 3:6a states, "For I am the LORD, I change not . . ."
    First, God is pictured in Romans 3:25,26 as being a "just" God.  If God is just then he must hate sin and all that goes with it, and must love that which is righteous.  That has not changed and Romans 11:22 defines this aspect of the nature of God, "Behold therefore the goodness and severity of God: on them which fell, severity; but toward thee, goodness, if thou continue in his goodness: otherwise thou also shalt be cut off."  That is a New Testament passage that paints what some would see as an Old Testament picture of God.
    Second, God is perfect as shown in Deuteronomy 32:4, II Samuel 22:31, and other passages.  How can anything that is perfect change?  Any change of a perfect thing would either make it more than perfect (which is like making a perfect circle more circular) or less than perfect (in which case there would be an imperfect God which the Scriptures deny).  God is perfect and for that reason His nature cannot change.
    Third, it is shown that God's nature has not changed by looking at specific examples in the Bible.  In the Old Testament God was not only severe but also loving as shown in one of the most beautiful of the Psalms:  Psalm 23.  Could a God who was loving not be described in that passage?  In the New Testament God was not only loving but also severe as shown in Matthew 21:12 where Jesus dealt harshly with the money changers in the temple.  There are other examples too numerous to mention.
    The question is not so much has the nature of God changed as it is how will the nature of God be toward us in judgment:  Will we live in such a way now that we are separated from Him eternally (severity), or will we obediently live so that we enjoy eternity in His presence (goodness)?