Note 10 at Ac 27:22: Paul was not speaking these things from his own intellect; he was saying, "thus saith the Lord." The angel of the Lord had told him that every person on the ship would be saved (Ac 27:24), yet Paul said that this prophecy would not come true if the centurion allowed certain sailors to try to escape in the lifeboat (Ac 27:31). Was Paul saying that an unmistakable word from the Lord could possibly not come to pass?

The Lord can and has made unconditional promises that only require His faithfulness to bring them to pass. But many promises of God are conditional. In this case, no conditions were stated, but apparently they were implied. Paul made it very clear that if the crew didn't comply with his instructions, they would die, contrary to what he was shown from the Lord and what he prophesied.

There is an Old Testament example of a prophecy from God not coming to pass also, because the person to whom the prophecy was made refused to obey God. Huldah, the prophetess, prophesied to King Josiah, in the name of the Lord, that he would die in peace (2Ch 34:28). For thirteen years Josiah had peace; however, he went to war with the king of Egypt when the king of Egypt clearly did not want to fight him. Necho, the king of Egypt, even said to Josiah, in the name of the Lord, that it was not God's will for them to fight, but Josiah went to battle anyway. Thus, Josiah died in battle, contrary to the word of the Lord (2Ch 35:20-24).

These examples reveal that the fulfillment of the word of the Lord can depend on our cooperation, even when that cooperation is not clearly stated as a condition.