Lk 24:25-27,32,44-45, Act 13:26-27, Acts 17:2-3, Acts 18:24-28, Acts 19:8-9, Acts 28:23,30-31
The Old Testament speaks of Christ. But if we don't explain it, people don't know if the Old Testament explains Christ. (Act 8:30-35, Acts 13:26-27)
Act 8:30 And Philip ran thither to him, and heard him read the prophet Esaias, and said, Understandest thou what thou readest? 31 And he said, How can I, except some man should guide me? And he desired Philip that he would come up and sit with him. 32 The place of the scripture which he read was this, He was led as a sheep to the slaughter; and like a lamb dumb before his shearer, so opened he not his mouth: 33 In his humiliation his judgment was taken away: and who shall declare his generation? for his life is taken from the earth. 34 And the eunuch answered Philip, and said, I pray thee, of whom speaketh the prophet this? of himself, or of some other man? 35 Then Philip opened his mouth, and began at the same scripture, and preached unto him Jesus.
Acts 13:26 Men and brethren, children of the stock of Abraham, and whosoever among you feareth God, to you is the word of this salvation sent. 27 For they that dwell at Jerusalem, and their rulers, because they knew him not, nor yet the voices of the prophets which are read every sabbath day, they have fulfilled them in condemning him.
Even Jesus' disciples did not know exactly about the Christ prophesied in the Old Testament. Jesus explained to them the Christ prophesied in the Old Testament, and He told them that that Christ was Himself. (Lk 24:25-27,32,44-45)
Lk 24:25 Then he said unto them, O fools, and slow of heart to believe all that the prophets have spoken: 26 Ought not Christ to have suffered these things, and to enter into his glory? 27 And beginning at Moses and all the prophets, he expounded unto them in all the scriptures the things concerning himself. 32 And they said one to another, Did not our heart burn within us, while he talked with us by the way, and while he opened to us the scriptures? 44 And he said unto them, These are the words which I spake unto you, while I was yet with you, that all things must be fulfilled, which were written in the law of Moses, and in the prophets, and in the psalms, concerning me. 45 Then opened he their understanding, that they might understand the scriptures,
Apollos zealously preached about Jesus, but did not say that Jesus was the Christ. After hearing the Priscilla and his wife's explanation, he said that Jesus was the Christ. (Acts 18:24-28)
Acts 18:24 And a certain Jew named Apollos, born at Alexandria, an eloquent man, and mighty in the scriptures, came to Ephesus. 25 This man was instructed in the way of the Lord; and being fervent in the spirit, he spake and taught diligently the things of the Lord, knowing only the baptism of John. 26 And he began to speak boldly in the synagogue: whom when Aquila and Priscilla had heard, they took him unto them, and expounded unto him the way of God more perfectly. 27 And when he was disposed to pass into Achaia, the brethren wrote, exhorting the disciples to receive him: who, when he was come, helped them much which had believed through grace: 28 For he mightily convinced the Jews, and that publicly, shewing by the scriptures that Jesus was Christ.
Paul went to the synagogue, explained the Christ prophesied in the Old Testament, and testified that that Christ was Jesus. (Acts 17:2-3)
Acts 17:2 And Paul, as his manner was, went in unto them, and three sabbath days reasoned with them out of the scriptures, 3 Opening and alleging, that Christ must needs have suffered, and risen again from the dead; and that this Jesus, whom I preach unto you, is Christ.
Paul testified that the entire Old Testament describes Christ and that Christ is Jesus. (Act 19:8-10, Act 28:23,30-31)
Act 19:8 And he went into the synagogue, and spake boldly for the space of three months, disputing and persuading the things concerning the kingdom of God. 9 But when divers were hardened, and believed not, but spake evil of that way before the multitude, he departed from them, and separated the disciples, disputing daily in the school of one Tyrannus. 10 And this continued by the space of two years; so that all they which dwelt in Asia heard the word of the Lord Jesus, both Jews and Greeks.
Act 28:23 And when they had appointed him a day, there came many to him into his lodging; to whom he expounded and testified the kingdom of God, persuading them concerning Jesus, both out of the law of Moses, and out of the prophets, from morning till evening. 30 And Paul dwelt two whole years in his own hired house, and received all that came in unto him, 31 Preaching the kingdom of God, and teaching those things which concern the Lord Jesus Christ, with all confidence, no man forbidding him.