Romans 3

Moses taught his people -

"...the LORD thy God will circumcise thine heart, and the heart of thy seed, to love the LORD thy God with all thine heart, and with all thy soul, that thou mayest live."  (Old Testament | Deuteronomy 30:6)

Obviously, circumcision was a token reminder of the law of Moses, but circumcision of the heart was not physical but spiritual.  In my mind, Moses was teaching that a change of heart, keeping His commandments, and loving God with all your soul was the key to eternal life.

Paul taught the same thing to the Roman Jewish converts -

"For he is not a Jew, which is one outwardly; neither is that circumcision, which is outward in the flesh:
29 But he is a Jew, which is one inwardly; and circumcision is that of the heart, in the spirit, and not in the letter; whose praise is not of men, but of God."  (New Testament | Romans 2:28 - 29)

King Benjamin declared to his people -

"...because of the covenant which ye have made ye shall be called the children of Christ, his sons, and his daughters; for behold, this day he hath spiritually begotten you; for ye say that your hearts are changed through faith on his name; therefore, ye are born of him and have become his sons and his daughters."  (Book of Mormon | Mosiah 5:7)

This is circumcision of heart by faith, entering into essential covenants of eternal life for -

"For all have sinned, and come short of the glory of God;
24 Being justified freely by his grace through the redemption that is in Christ Jesus..."  (New Testament | Romans 3:23 - 24)

Thus Paul concludes -

"Do we then make void the law through faith? God forbid: yea, we establish the law."  (New Testament | Romans 3:31)

I believe Nephi summarized it best -

"For we labor diligently to write, to persuade our children, and also our brethren, to believe in Christ, and to be reconciled to God; for we know that it is by grace that we are saved, after all we can do."  (Book of Mormon | 2 Nephi 25:23)