(Matthew 5:17) “Do not think that I came to destroy the Law or the Prophets. I did not come to destroy but to fulfill.After His resurrection He instructed His disciples from all of the Scriptures - showing how they taught about Him.
(John 5:39 NKJV) You search the Scriptures, for in them you think you have eternal life; and these are they which testify of Me.
(Luke 24:25-27) Then He said to them, “O foolish ones, and slow of heart to believe in all that the prophets have spoken!One point about this is that even though Paul said he was determined to know nothing among the Corinthians except "Jesus Christ and Him crucified," it does not mean that he only said those five words over and over again. (1Corinthians 2:2)
26 Ought not the Christ to have suffered these things and to enter into His glory?”
27 And beginning at Moses and all the Prophets, He expounded to them in all the Scriptures the things concerning Himself.
The whole Bible is about Jesus Christ and Him crucified. What Paul means is that he wasn't relying on human philosophy or rhetoric to win people to the message of the Gospel. At the same time he WAS teaching and preaching about Christ from the scriptures.
A second point is that we should never preach from the Bible without looking at how it points to Christ. Any attempt to change people's moral behavior that doesn't involve the Gospel of Jesus Christ amounts to man made religion of human works.
Graeme Goldsworthy in Preaching The Whole Bible As Christian Scripture asks, "Can I Preach a Christian Sermon without Mentioning Jesus?" Part of his answer is:
Any sermon, then, that aims to apply the biblical text to the congregation and does so without making it crystal clear that it is in Christ alone and through Christ alone that the application is realized, is not a Christian sermon. It is at best an exercise in wishful and pietistic thinking. It is at worst demonic in its Christ-denying legalism.Amen! Let us preach Christ!