How can we trust the validity of Jesus being the saviour?

I love what Jesus taught. The peace, love, understanding part. I was just meaning that since he knew all the scriptures and prophecies, he knew what was expected. Like when Jesus said "Let righteousness be fulfilled" and rode into Jerusalem on a donkey, because this was a prophecy. If someone knows what is expected, how can it be trusted. Wouldn't prophecy be more believable if the subject didn't know about the prophecies? People who know what has been foretold would just have to do what has been said.