Some, on reading the portion of letter of Paul to the Galatians wondered about their faith. Not their own faith in Christ, but the manner and form of the faith of Old Testament folk. What was it that they believed, or in whom did they believe? This is a foundational question because on it hinges our understanding of salvation and our need for mission and mercy work around the world.
Galatians 3:23-24New King James Version
23 But before faith came, we were kept under guard by the law, kept for the faith which would afterward be revealed. 24 Therefore the law was our tutor to bring us to Christ, that we might be justified by faith.
The promise to the Patriarchs, the message of the Prophets, the Exodus, the Tabernacle in the wilderness and the Temple in Jerusalem were all a part of a gospel message that told of the sufferings of the Messiah and the glories that would follow. All of these messages pointed to faith in the One who would come. Peter says that the prophets studied their own utterances and writings to come to grips with the revelations that God had given them.
1 Peter 1:10-12New King James Version (NKJV)
10 Of this salvation the prophets have inquired and searched carefully, who prophesied of the grace that would come to you, 11 searching what, or what manner of time, the Spirit of Christ who was in them was indicating when He testified beforehand the sufferings of Christ and the glories that would follow. 12 To them it was revealed that, not to themselves, but to us they were ministering the things which now have been reported to you through those who have preached the gospel to you by the Holy Spirit sent from heaven—things which angels desire to look into.
Jesus explains the Old Testament as being about Him. Remember that when Jesus talked about the Scriptures He was talking of the Old Testament.
Then He said to them, “O foolish ones, and slow of heart to believe in all that the prophets have spoken! Ought not the Christ to have suffered these things and to enter into His glory?” And beginning at Moses and all the Prophets, He expounded to them in all the Scriptures the things concerning Himself. (Luke 24:25–27)
Jesus on the road to Emmaus explains to discouraged disciples that the Old Testament Bilbe was all about His suffering death and resurrection.
Later in the same chapter, Jesus speaks again.
Then He said to them, “These are the words which I spoke to you while I was still with you, that all things must be fulfilled which were written in the Law of Moses and the Prophets and the Psalms concerning Me.” And He opened their understanding, that they might comprehend the Scriptures. Then He said to them, “Thus it is written, and thus it was necessary for the Christ to suffer and to rise from the dead the third day, and that repentance and remission of sins should be preached in His name to all nations, beginning at Jerusalem.” (Luke 24:44–47)
The disciples get it ……….
But those things which God foretold by the mouth of all His prophets, that the Christ would suffer, He has thus fulfilled. Repent therefore and be converted, that your sins may be blotted out, so that times of refreshing may come from the presence of the Lord, and that He may send Jesus Christ, who was preached to you before, whom heaven must receive until the times of restoration of all things, which God has
spoken by the mouth of all His holy prophets since the world began. (Acts 3:18–24)
So Old Testament faith was in a person who was to come called Messiah or Christ. New Testament faith is faith in the one that has come called Jesus the Christ.
Finally the Old Testament saints that sing songs around Christmas time bear witness to what their faith was and in whom they believed. See the songs of Zechariah, Simeon and Mary, and note the tremendous missionary and mercy emphasis.