Jesus had stated something concerning what was written in the OT this way
John 5:46 For had ye believed Moses, ye would have believed me: for he wrote of me. But if ye believe not his writings, how shall ye believe my words?
Like, if they believed Moses (his writings) which testified of Christ you would actually believe Christs words, since Moses as a servant, was for a testimony of those things which were to be spoken after Hebrews 3:5 as is shown in Deuteronomy 18:18 and confirmed by Christ in John 12:49
So, had ye believed Moses, ye would have believed me
These testify of Jesus Christ
Luke 24:44 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.
Acts 28:23 show Paul testifying, "persuading them concerning Jesus, both out of the law of Moses, and out of the prophets, from morning till evening".
So the people were being persuaded of Jesus Christ out of the law of Moses and the prophets.