He has helped his servant Israel, in remembrance of his mercy.
(Luke 1:54 ESV)
Here is the fulfillment of all mercies. There is no forgiveness apart from Jesus Christ and him crucified. There is no true knowledge of God apart from him. There is no blessing apart from him. As the apostle Paul puts it in 2 Corinthians 1:20 (KJV): “For all the promises of God in him are yea, and in him Amen, unto the glory of God by us.” “He hath holpen his servantIsrael.” Israel is the seed of Abraham. Yes, but under the law and condemned by the law. Not able to be free; held in bondage and in captivity; living on the promises, thank God, but nothing more.
But here is the great fulfillment; and so you will find all the Old Testament prophets, psalmists, and seers have seen this. They are looking forward; they know that this is what will fulfill all the promises and bring the mercy into the individual experience. It is all in and through our Lord and Savior Jesus Christ and what he did when he was in this world, and what he is now continuing and applying in the glory.
What God did when he sent his Son into the world is an absolute guarantee that he will do everything he has ever promised to do. Look at it in personal sense: “All things work together for good to them that love God”—that is a promise—“to them who are the called according to his purpose” (Rom. 8:28, KJV). “But how can I know that is true for me?” asks someone. The answer is the incarnation. God has given the final proof that all his promises are sure, that he is faithful to everything he has ever said. So that promise is sure for you. Whatever your state or condition may be, whatever may happen to you, he has said, “I will never leave thee, nor forsake thee” (Heb. 13:5, KJV)—and he will not. He has said so, and we have absolute proof that he fulfills his promises. He does not always do it immediately in the way that we think. No, no! But he does it! And he will never fail to do it.
From Come, Thou Long-Expected Jesus: Experiencing the Peace and Promise of Christmas, edited by Nancy Guthrie