Line 10's > "Buckle!" is the most debated verb in Victorian poetry. Buckle as collapse: all that brute beauty and valor might break under pressure. Buckle as clasp: like a knight fastening armor, the bird's qualities join together. Hopkins likely meant both simultaneously.
The poem dedicates itself > "To Christ our Lord" but waits until line 10 to make the turn explicit with > "O my chevalier!" (French for knight). The falcon becomes Christ the warrior-knight, and the fire that breaks from him is the Incarnation—God's glory revealed through physical stress, through buckling.
The final three lines prove this with two examples: the plough blade shines when it's doing its hardest work (cutting earth), and embers glow gold-vermillion when they fall and break apart. Hopkins is arguing that stress reveals hidden glory—the falcon's beauty emerges in the difficult hover, Christ's divinity blazes brightest at the Crucifixion. > "Fall, gall themselves, and gash" uses three violent verbs for embers, but the result is gold-vermillion, the colors of dawn and of sacred art.