Is the last line of on his blindness a paradox.... How?

Yes, the last line of John Milton's poem "On His Blindness" presents a paradox. It suggests that serving God is not limited to visible or active contributions, as the speaker grApples with his blindness and feelings of inadequacy. The line implies that even in perceived limitations, one can still fulfill their purpose, highlighting the idea that divine service transcends physical abilities and is rooted in faith and inner commitment. This juxtaposition of ability and service creates a thought-provoking tension within the poem.