All Scripture reveals God redemptive solution for man. Not every Scripture reveals it evenly however. Some passages are in full bloom and give the plain, clear account of Christ’s work on the cross for our sins. Other passages (most Old Testament passages) are in seed-form that are in some way connected to the mature message of God’s redemption. Bryan Chapell, of Covenant Seminary, provides a vivid illustration in his book Christ Centered Preaching.
You do not explain what an acorn is, even if you say many true things about it (e.g., it is brown, has a cap, is found on the ground, is gathered by squirrels), if you do not in some way relate it to an oak tree. In a similar sense, preachers cannot properly explain a seed of biblical revelation, even if they say many true things about it, unless they relate it to the redeeming work of God that all Scripture ultimately purposes to disclose.
And later, he writes:
Christ-centered preaching rightly understood does not seek to discover where Christ is mentioned in every text but to disclose where every text stands in relation to Christ.