If you believed the prophecies of the first coming of Jesus, it would and did change your behavior. The prophecies told that certain things would happen, but did not tell when these things would happen.

Moreover many of the prophecies were given in such a form that, if you didn’t look carefully at the prophecies, and think them through, or if you didn’t carefully compare them with the rest of Scripture, you would never get it. Further it seems that God knew that some of the prophecies would not be understood before the fact.

For instance, Jesus resurrection is implied, but not stated,
in both Psalm 22 and Isaiah 53

For instance, Jesus death is clearly described in Psa 22:14-15, etc. So His death and suffering should have been understood. But the resurrection? After describing His death, there is a cry for help in Psa 22:21. Then it describes this crucified Savior as declaring God’s name in the assembly in Psa 22:22, 25, and it says God answered in pray in Psa 22:24! But how? Didn’t He just die in verses 14-15? So some sort of release from death is described, but not clearly.

Similarly, Isaiah 53 it describes the judicial murder of the Savior in Isa 53:4-8. In verse 8 He is clearly “cut off out of the land of the living,” and in verse 9 He was “with a rich man in his death.” Then after describing His death it says,

“… he shall see his seed, he shall prolong his days, and the pleasure of Yahweh shall prosper in his hand.”
Isa 53:10

But how? Didn’t He just die? So an escape from death one way or another is clearly implied. Similarly Jesus told his disciples of His coming suffering and resurrection, but it went clear over their heads, much as current prophecies may go over your head and mine! The closest to catching some of this was by Jesus enemies. The chief priest and scribes told Pilate,

“63 … “Sir, we remember what that deceiver said while he was still alive: ‘After three days I will rise again.’ 64 Command therefore that the tomb be made secure”
Mtt 27:63-64

So what was the intended function of these prophecies which it seems were deliberately obscure? It seems they were intended to authenticate Jesus life, after the fact! After the fact, all of this would have been clear.

Still much of it was very clear.

There were many passages like,

“Then the eyes of the blind shall be opened, and the ears of the deaf shall be unstopped.”
Isa 35:5

It didn’t take a PhD in biblical studies for the crowds to see the point of Jesus healing people. So many saw and understood that Jesus was the Messiah, the Christ of God!

Key Point: you don’t have to understand EVERYTHING,
to get enough to save your life!

Many things are told from multiple points of view, so if you don’t get it one way, you may get it another way. Few got it all. Many got enough to save their souls.

Scriptures are from the World English Bible (WEB), a copyright free revision of the original ASV American Standard Version 1901