Acts13:26 Men, brothers, sons of the race of Abraham, and those among you who fear God, to us the word of this salvation has been sent forth. (29~30) And when they had accomplished all that was written concerning Him, they took Him down from the tree and laid Him in a tomb. But God raised Him from the dead.
The Old Testament contains many things: history, the law, types, and prophecies. The Jews studied the Old Testament week by week, but they did not pay attention to Christ. They had some thought concerning the Messiah, but they did not have any understanding of Christ.
When Paul went into the synagogues to preach and teach, he did not care for anything other than Christ. When some hear that Paul preached Christ and Christ alone, they may say, "Did Paul not begin his preaching with an account of the history in the Old Testament? Did he not speak of God's bringing His people out of Egypt, and about Saul and David?" Yes, Paul spoke about those things, but he did so in order to prepare the way to preach Christ.
In verse 22 Paul quoted the word about David being a man according to God's heart. Then in verse 23 he went on to say, "From this man's seed, God, according to promise, brought to Israel a Savior, Jesus." Here we see that after a short introduction, he came to his crucial message, which is altogether centered on Christ.
After beginning with the history until the time of David, Paul went on to point out that from David's seed God brought forth a Savior, Jesus Christ. With Him there is salvation.