Listen how Paul explains this phenomenon about choice in the next chapter of Romans:
. . . for until the Law, sin was in the world; but sin is not imputed when there is no law —Romans 5:13
In other words, did sin and evil exist before the Torah was given to Moses on Mt. Sinai? Of course it did. However, until God set down His regulations for Israel, there were no regulations to break. One way of looking at this is that Israel lived as Adam and Eve; the Hebrews had wills, so now they needed choices set before them so they could use their wills. Once God set down His rules, His Law, His Torah, Israel had to face moral choices as defined by God. They could choose whether to love Him, and demonstrate it by obedience to His Torah—or they could choose not to love Him, and demonstrate that by disobeying His Torah.
All of which causes Paul to conclude this:
Why the Law then? It was added because of transgressions, having been ordained through angels by the agency of a mediator, until the seed should come to whom the promise had been made —Galatians 3:19
This verse is often stated to mean “Why the Law, then? It was added to create transgressions . . .” And, that’s true. If man has a will, he must also have moral choices set before him. The Law provides for those moral choices.
The whole point of this is that if there were no moral choices—if somehow there was nothing but good—then having a will would be totally meaningless. It would be a lot like a Cuban election; you can vote for Castro, or you can vote for Castro. You cannot even choose not to vote. What meaning is there to the concept of “election” if there are no choices? It is the same for the human will. Without moral choices being available, the purpose for a will is made null and void. So . . .
The whole thing, then, is a matter of faith on man’s part and generosity on God’s. He gives the security of his own promise to all men who can be called “children of Abraham,” that is, both those who have lived in faith by the Law, and those who have exhibited a faith like that of Abraham. To whichever group we belong, Abraham is in a real sense our father, as the scripture say:
A father of many nations have I made thee.
This faith is valid because of the existence of God himself, who can make the dead live, and speak his Word to those who are yet unborn —Romans 4:16-17
If interested, you can download the entire study of The Letter to Christians at Rome