To fulfill something is to make it come true. None of us chooses our own family line and place of birth. None of us can choose to return to life after dying. But Jesus boldly claimed to fulfill all Old Testament prophecies about the Messiah. To His own followers Jesus said,
“O foolish ones, and slow of heart to believe all that the prophets have spoken! Was it not necessary that the Christ should suffer these things and enter into His glory?” And beginning with Moses and all the Prophets, He interpreted to them in all the Scriptures the things concerning Himself … Then He said to them, “These are My words that I spoke to you while I was still with you, that everything written about Me in the Law of Moses and the Prophets and the Psalms must be fulfilled” (Luke 24:25-27, 44).
To the leading Jews He said,
“… it is they [Scriptures] that bear witness about Me… For if you believed Moses, you would believe Me; for he wrote of Me” (John 5:39, 46).
This continued to be the message of the early Christians (Acts 3:24; 10:43; 13:32; 26:22-23).
Paul went in, as was his custom, and on three Sabbath days he reasoned with them from the Scriptures, explaining and proving that it was necessary for the Christ to suffer and to rise from the dead, and saying, “This Jesus, whom I proclaim to you, is the Christ” (Acts 17:2-3).