What Herbert is saying in this poem is that it is the stresses of every day life that are going to bring us closer to God. He is saying that God knows that and that is why he does not give us "rest" alone out of all the gifts he could have given us.
Herbert envisions God giving out gifts and wondering how exactly to make people. He envisions God deciding that the best way to make us seek him is to deprive us of rest. By saying this, he is saying that we turn to God when we are tired, stressed, and in need. This may not say good things about us, but it does seem to be the truth.
“The Pulley” is an excellent poem for the illustration of imagery because of its graphic title and emblematic comparison of mechanics and salvation. Readers who are artistic may be able to draw a sketch of a pulley for the benefit of their appreciation. If any reader of physics knows about the mechanical advantage of pulleys, the reader may be at a significant advantage in understanding the poem. Herbert is building the poem on the faith that God accepts humankind unconditionally; his phrase “repining restlessness” (line 17) describes the anxiety prior to this acceptance. Herbert emphasizes “weary” and “weariness” here as the accompanying condition of the search. Weariness is a recurring Biblical word and concept.