Tho' truths in manhood darkly join, Deep-seated in our mystic frame, We yield all blessing to the name Of Him that made them current coin;
For Wisdom dealt with mortal powers, Where truth in closest words shall fail, When truth embodied in a tale Shall enter in at lowly doors.
And so the Word had breath, and wrought With human hands the creed of creeds In loveliness of perfect deeds, More strong than all poetic thought;
Which he may read that binds the sheaf, Or builds the house, or digs the grave, And those wild eyes that watch the wave In roarings round the coral reef.
This one's a bit tough to suss out. Stick with us here.
In the first stanza, the speaker brings up truths that "darkly join" within humans. This might mean that humans can't figure these things out. They struggle (like the speaker has been doing so far), but these things remain "dark" and buried in our "mystic frame" (probably meaning the Soul).
But Jesus (as the embodiment of God, the Creator) demonstrates these truths. He is the "truth embodied in a tale / enter[ed] at lowly doors" (731-732).
This means he came from lowly beginnings, but then became the embodiment of the Word (the truth from the Bible).
Because of Jesus, even those who work lowly jobs (like harvesting, or building, or grave-digging) can "read" the world for these bigger spiritual truths that can be seen in nature.