The first question is, “faithful” to what or to whom?” The answer might truly astonish us, if we have never considered before the full implications of words by Saint Paul, “For there is one God, and one mediator between God and men, the man Christ Jesus.”1 God is faithful to God, God is faithful to Man, and God is faithful to His own promise.
That God is faithful to God means that God the Father is faithful to God the Son, which is ultimately the true meaning of God being faithful to Man and to His own promise. For the Man Christ Jesus is God the Son, the only Mediator between God and man; and he is the Mediator of the New Covenant.
Comparing the ministry of Jesus Christ to that of Moses, the writer to the Hebrews says, “But now hath he obtained a more excellent ministry, by how much also he is the mediator of a better covenant, which was established upon better promises.”2 The people of the Covenant God made with Israel through Moses at Mount Sinai, were promised possession of the Land and peace therein, as long as they lived by the words of the Law. But, about the better promises of the better covenant, the writer to the Hebrews goes on to quote the words of the Prophet Jeremiah.
“Behold, the days come, saith the LORD, that I will make a new covenant with the house of Israel, and with the house of Judah: Not according to the covenant that I made with their fathers in the day that I took them by the hand to bring them out of the land of Egypt; which my covenant they brake, although I was an husband unto them, saith the LORD: But this shall be the covenant that I will make with the house of Israel; After those days, saith the LORD, I will put my law in their inward parts, and write it in their hearts; and will be their God, and they shall be my people. And they shall teach no more every man his neighbour, and every man his brother, saying, Know the LORD: for they shall all know me, from the least of them unto the greatest of them, saith the LORD; for I will forgive their iniquity, and I will remember their sin no more.”3
Those last words of that long list of promises, that God will forgive the iniquity of His people and remember their sin no more, belong to all who have been justified by the faith of Abraham, that is all who believe in the Gospel of the Lord Jesus Christ.4 This promise is made by the hand of the One Mediator between God and men. It is a promise to us through the Son, and therefore a transaction between God the Father and God the Son, enacted within the people of the Church by the Holy Spirit. It is not the result of a human idea, and not the result of our own pleading. God has promised God, and God is therefore faithful to God, to Man and to His word.
“If we say that we have not sinned, we make him a liar, and his word is not in us. My little children, these things write I unto you, that ye sin not. And if any man sin, we have an advocate with the Father, Jesus Christ the righteous: And he is the propitiation for our sins: and not for ours only, but also for the sins of the whole world.”5
Therefore, God is just to forgive, as Paul tells us: