Romans 5:20
Moreover the law entered that the offense might abound. But where sin abounded, grace abounded much more,

The first law involved not eating a certain fruit from a certain tree. It was a single law and against an infinite freedom.
They chose to break the law.
Previous to our scripture Paul states that death reigned from Adam to Moses, even without the Law. The wages and penalty for sin is death.
Then came the Mosaic Law and sin abounded as it became defined.
But sin cannot abound more than grace.
God’s grace can cover any sin you can dish out.
Just because God give grace to cover sin, is not an excuse to sin but a reason not to sin.
That is understood more clearly in the next chapter.