Why did Jesus not Preach the Gospel?

As Jesus started on his way, a man ran up to him and fell on his knees before him. “Good teacher,” he asked, "what must I do to inherit eternal life?”
--Mark 10:17

Someone may ask: "Why did Jesus not say to believe in my death and resurrection as a propitiation for your sin"?

There are many responses.
[1]

12 “I have yet many things to tell you, but you can’t bear them now. 
13 However when he, the Spirit of truth, has come, he will guide you into all truth, for he will not speak from himself; but whatever he hears, he will speak.”
--John 16:12

This can be interpreted to mean that the full gospel message would be revealed when the holy spirit would be sent.  (Note some Muslims take this as foretelling Mohammed and the Quran).

[2]
  Here is one answer to this is articulated by Paul.

None of the rulers of this age knew this wisdom, for if they had known it, they would not have crucified the Lord of glory.
--1 Cor 2:8

Here the "rulers of this age" refers to the demonic rulers, not any human beings.

[3]
     But while everyone was marveling at all that He was doing, He said to His disciples, 44“Let these words sink into your ears; for the Son of Man is going to be delivered into the hands of men.” 45But they did not understand this statement, and it was concealed from them so that they would not perceive it; and they were afraid to ask Him about this statement.
--Luke 9:43
First Jesus tells them something, but then it is concealed from them.  Why, then say it in the first place?  Because they would understand it after his resurrection.


[4]
Here is another response: Jesus actually did preach the gospel! In this passage Paul says he received what Jesus taught directly from Jesus.

23 For I received from the Lord that which I also delivered to you, that the Lord Jesus in the night in which He was betrayed took bread; 
24 and when He had given thanks, He broke it and said, “This is My body, which is for you; do this in remembrance of Me.” 
25 In the same way He took the cup also after supper, saying, “This cup is the new covenant in My blood;”

Also:
11 For I would have you know, brethren, that the gospel which was preached by me is not according to man. 
12 For I neither received it from man, nor was I taught it, but I received it through a revelation of Jesus Christ.
--Gal 1:11-12

Here again Paul says he received his gospel directly from Jesus.

Also:
Peter was shown that the that the Gentiles are to be part of the Church in a vision in Acts 10:10-17

Also:
The entire book of Revelation was revealed to John after the death and resurrection of Jesus.