Hopkins, a Jesuit priest, followed the Romantic poets in understanding all of creation as an expression of the divine. We learn about the nature of God, Hopkins believed, as we watch the glory his his creation unfold all around us.
Therefore, in Hopkins's hand, the flight of a windhover becomes more than just a natural phenomenon. In the first stanza, only the flight is described, but it is described in majestic terms. Hopkins's speaker personifies the windover, describing it as if it is a member of royalty. He likens it to a dauphin, the son and heir of a French king. It rides the currents of the air as a proud royal might ride a steed. The speaker describes the bird as experiencing "ecstasy" as it "reins" in the wind and hovers in the air. The speaker is in awe of the bird.
However, while this exercise of grace and mastery delights the speaker, the true power of the bird emerges in the second stanza. Here, Hopkins moves to the spiritual plane. The bird is likened to Christ in its ability to "buckle" or stand still, pulling all the forces of its princely nature into submission in its stillness. At this moment, a deeper, more spiritual power "breaks" (a pun on brakes) from the bird as it hovers. It becomes Christ like and hence a "billion" times "lovelier" and "more dangerous" than it was in comparison to a mere royal. This expresses the central Christian paradox that there is a spiritual power far greater than worldly power in submission and stillness.
In the third stanza, the speaker comments that this is not singular or unique to the bird, as God's power flames forth in many ways.
Interestingly, except for the dedication of the poem "To Christ our Lord," Hopkins does not directly invoke God in the poem, yet it is infused with a sense of the sacred quality of the earth.