Donald Juel, in Messianic Exegesis: Christological Interpretation of the Old Testament in Early Christianity, points out that the New Testament documents were written in response to various situations and needs. Those for whom the documents were written already had significant knowledge of Jesus and how the Old Testament spoke of Him, and therefore there is a lot of important information about Jesus that is assumed in the documents rather than explicitly stated. Here is part of how he opens his second chapter:
The NT contains not a single essay on Christology, not one christological commentary on an OT book or even a portion of a book. It includes narratives, letters, and an apocalypse; even the earliest of these was composed well after most of the basic exegesis of the OT had been completed. Paul’s letters give evidence of a wealth of interpretive traditions, only a small portion of which he chooses to quote or comment on explicitly. The notable absence of christological exegesis in his letters reveals less a lack of interest in the topic than a general approval of the formulations he inherited from the tradition. There may well be OT passages that were foundational to the development of exegetical constructions that are never cited, either because their presence could be taken for granted or because their major function was to provide links with other, more readily applicable portions of the Scriptures.
If we want to allow the Holy Spirit to lead and guide us into all the truth about Jesus, we have to acknowledge rightly the form in which some of that truth comes to us.