Answer and Explanation:
Line 20 contributes to the development of the poem because it is in it that the speaker questions God's creations.
In the poem "Tyger" by William Blake, the speaker is expressing his admiration over how ferocious and powerful a tiger is. Yet, in line 20, he asks "Did He who make the Lamb make thee?" That question the true purpose of the poem. Even though all of God's creations deserve admiration, it is odd that he would create both, good and evil. The tiger represents our capacity to sin, while the lamb represents our goodness and innocence. Line 20, therefore, questions the corruption of the world.