One of the great men “of old” was Moses, and Moses received the law directly from God. This was a tremendous act of communication with God, and a powerful witness to the reality of God. This ties the name of Moses to the men “of old” in the previous verse. However, great as Moses was, it is the Christ who has fulfilled that great law, and given another. This Atoning Messiah also appeared to the Nephites, and bears definitive witness to the reality of God.
[by faith that it hath been fulfilled]: The “gift of his Son” is what is fulfilled through faith. The atonement is a gift to us, but one which we must actively accept. Therefore, it is through our faith that the promise of the gift is fulfilled. The atonement can become the greater way, but only if we have the faith to accept the atonement, and follow the way the Savior outlined.