The definition of Grace is unmerited favor. The dispensation of Grace began with Abraham.

For if Abraham was justified by works he has something to boast about, but not before God. For what does the scriptures say? "Abraham believed God and it was Reckoned to him as Righteousness.

Romans 4:2-3

The purpose was to make him the Father of all who believed without being circumcised and who thus have Righteousness Reckoned to Them.

Romans 4:11

No distrust made him waver concerning the promise of God, but he grew strong in his faith as he gave glory to God, fully convinced that God was able to do what he had promised.

Romans 4:20-21

The Law, which came four hundred and thirty years afterward does not annul a covenant previously ratified by God, so as to make the promise void. For if the inheritance is by the law, it is no longer by promise: but God gave it to Abraham by a promise. Why then the Law? It was added because of transgressions, til the offspring should come to whom the promise had been made.

Galatians 3:17-19

Now before Faith came, we were confined under the Law, kept under restraint, until faith should be revealed. So the Law was our custodian until Christ came, that we might be justified by faith.

Galatians 3:23-24

Likewise my brethren, you have Died to the Law through the body of Christ so you may belong to another, to him who has been raised from the dead in order that we may bear fruit for God. But now we are discharged from the Law, dead to that which held us captive, so that we serve not under the old written code but in the New Life of the Spirit.

Romans 7:4,6

By abolishing in His flesh the Law of Commandments and ordinances, that he might create in himself one new man…

Ephesians 2:15

On one hand, a former commandment is set aside because of its weakness and uselessness (for the Law made nothing perfect;)…

Hebrews 7:18-19

Our sufficiency is from God, who has qualified us to be ministers of a new covenant, not in a written code, but in the Spirit, for the written code Kills but the Spirit gives Life.

2 Corinthians 3:5-6

I believe Paul sums it up in Galatians, when he said:

You are Severed from Christ, you who would be justified by the Law; you have fallen from Grace.

Galatians 5:4