When you are preaching the Old Testament, there should always be a radar bleeping in your heart regarding where Christ fits into the message. Some will suggest that every message must be entirely and purely about Christ, whatever the text was originally intended to convey. I feel this approach can bring our view of the inspiration of Scripture into disrepute.
Not every Old Testament passage is just about Christ. I know that Jesus took two disciples on a tour of the Old Testament on the road to Emmaus, but I’d also like to point out that that road is only 7 miles long! We need to recognize that many passages are about humanity responding to the God of the covenant, or about the power of the creator God, or about judgment, etc. If it is a stretch to make the passage be about Jesus, don’t. However,
The listeners are always listening to the sermon post-incarnation. Consequently there is a need to make sure we are engaging with the text in light of later revelation. That doesn’t mean we have to reinterpret the original meaning to be something that it could not have been originally. But we do have to land the bridge of the message in the contemporary circumstance of our listeners (including the fact that we are post-incarnation, post-cross, post-resurrection, post-Pentecost, etc.)
The Old Testament is, of course, heading toward Christ. It is Christo-telic. That doesn’t mean it is Christo-exclusive.
May God grant us wisdom as we seek to honour His whole revelation in all its fullness, recognizing the progression of revelation, speaking with absolute relevance to contemporary listeners and always honouring and glorifying the Word incarnate!