In the name of the Father and of the +Son and of the Holy Spirit, Amen.
If Jesus Christ is the same yesterday, today, and forever (Heb. 13:8) then there are not two different gods described in the Bible, one in the Old Testament and one in the New Testament. There is merely the same God, with the same character throughout all of time. He has different testaments or legal frameworks which have set out different boundaries and ways of working, but He is the same. For example, under the New Testament in His blood (Matt. 26:26-28) there is no longer a physical temple in Jerusalem (1 Cor. 3:16; Eph. 2:20-22) with the sacrifices and rules of cleanness in order to enter it. But while the specifics may be different, the big picture is the same. God’s character is the same. God still has the same goal: your salvation.
Which brings us to today’s question: why was Abel’s sacrifice accepted and Cain’s not? Over the years I’ve heard many answers, but none of them ever made much sense. For instance, I’ve heard it said that Cain’s sacrifice was of the “fruit of the ground” (Gen. 4:3) which leads some people to speculate that it was rotten fruit from off the ground. That Cain was not giving his best to God. He was not giving of his first (or best) fruits.