As far as prophecies are concerned, for the Christian these are mandated by the biblical text.  For example, the following OT text clearly shows that God revealed his will long before He took action against Israel for their sins:

Isaiah 46:8-11 (ESV)
8 Remember this and stand firm, recall it to mind, you transgressors, 9 remember the former things of old; for I am God, and there is no other; I am God, and there is none like me, 10 declaring the end from the beginning and from ancient times things not yet done, saying, ‘My counsel shall stand, and I will accomplish all my purpose,’ 11 calling a bird of prey from the east, the man of my counsel from a far country. I have spoken, and I will bring it to pass; I have purposed, and I will do it.

In addition, the OT clearly shows that God announced all that he was going to do to his servants the prophets:

7 "For the Lord God does nothing without revealing his secret to his servants the prophets. Amos 3:7 (ESV)

Thus we read, time and again, how Israel ignored the prophets whom God sent.  God sent these prophets to warn His people of what would happen if they refused to repent, but they would not listen (2 Kings 17:13-14; Jer 7:25-26; 26:5; 29:19; 35:15-16; 44:4-5).

In the same manner, the prophecies about Christ, though denied by Liberal Protestantism Scholars, unbelieving Jews, people of Islam, and atheists, are mandated by the biblical text.  Jesus Himself mandates these very prophecies:

25 And he said to them, "O foolish ones, and slow of heart to believe all that the prophets have spoken! 26  Was it not necessary that the Christ should suffer these things and enter into his glory?" 27 And beginning with Moses and all the Prophets, he interpreted to them in all the Scriptures the things concerning himself. Luke 24:25-27 (ESV)
44 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." 45 Then he opened their minds to understand the Scriptures, 46 and said to them, "Thus it is written, that the Christ should suffer and on the third day rise from the dead, 47 and that repentance and forgiveness of sins should be proclaimed in his name to all nations, beginning from Jerusalem. Luke 24:44-47 (ESV)

Therefore, we must exercise due diligence to show these prophecies forth in the biblical texts, no matter how much the detractors object.  For I cannot accept their objections if Jesus Himself says that the "Law of Moses and the Prophets and the Psalms" speak of Him.