Acts 13:21-25
Acts 13:21 (KJB)
And afterward they desired a king: and God gave unto them Saul the son of Cis, a man of the tribe of Benjamin, by the space of forty years.
Next Paul had reminded his hearers that Israel wanted to be like the surrounding nations in that they wanted a king to rule over them. God gave them their request and chose Saul the son of Kish to be their first king. Saul had reigned over Israel for 40 years, was the first king of the United Israel, of all twelve tribes. Paul was not just giving a history lesson to these people, instead he was emphasizing through his narrative that God was guiding the history of Israel.
Acts 13:22 (KJB)
And when he had removed him, he raised up unto them David to be their king; to whom also he gave testimony, and said, I have found David the son of Jesse, a man after mine own heart, which shall fulfil all my will.
Saul had become so wicked that he even trusted the counsel of a witch. That was shortly before Saul was killed in battle and then David became the official king of Israel. David was a saved man although not a perfect man. (1 Sam 13:14 KJV) But now thy kingdom shall not continue: the LORD hath sought him a man after his own heart, and the LORD hath commanded him to be captain over his people, because thou hast not kept that which the LORD commanded thee. David was the second king of United Israel and ruled for 40 years.
Acts 13:23 (KJB)
Of this man's seed hath God according to his promise raised unto Israel a Saviour, Jesus:
God had given David a promise in 2 Samuel 7:11-16 that He was going to establish the Throne of David forever. That promise of an eternal throne would come to pass about a thousand years later when the Lord Jesus Christ would be born of Mary who was in the lineage of David, thus fulfilling the promise of that Eternal Davidic covenant. Paul now tells his hearers that it was all fulfilled because Jesus had already come to earth, paid the penalty for sins, and was the prophesied Savior. The eternal covenant was the Gospel of Grace.
Acts 13:24 (KJB)
When John had first preached before his coming the baptism of repentance to all the people of Israel.
Paul now brings up the ministry of John the Baptist who first preached the baptism of repentance to all of Israel. John was the one who had the privilege of introducing the Lord Jesus Christ at His baptism. John had awakened the sleeping nation of Israel to the fact that they needed repentance. Many in Israel were awaiting the consolation of Israel, that is, the coming Messiah.
Acts 13:25 (KJB)
And as John fulfilled his course, he said, Whom think ye that I am? I am not he. But, behold, there cometh one after me, whose shoes of his feet I am not worthy to loose.
(John 1:19-20 KJV) And this is the record of John, when the Jews sent priests and Levites from Jerusalem to ask him, Who art thou? {20} And he confessed, and denied not; but confessed, I am not the Christ. Those who came to hear John and see him baptize were wondering whether he was the prophesied Messiah or not. John had totally denied that he was the Christ but stated that the one who will come after him will be the Messiah and John was not worthy enough to untie the sandals from his feet. John knew that he was the forerunner for the Christ and he did not pretend to be more than he was.