Here's a summary:
* The speaker addresses God, describing how He has given humans a variety of good things: These blessings include beauty, joy, and love.
* However, the speaker then describes how God has withheld a final element, "a restless, unenjoying thought": This is a kind of dissatisfaction, a longing that drives humans to search for something more.
* This "thought" serves as a "pulley": It pulls humans towards God, creating a desire for Him that transcends earthly pleasures.
* The poem concludes with a statement that the "thought" is the best blessing of all: It is through this longing that humans can truly experience God's love and find lasting happiness.
The poem suggests that human happiness is not found in simply possessing earthly goods, but rather in a deeper, spiritual connection with God. This connection is achieved through a state of "restless, unenjoying thought" which drives humans to seek God's love and presence.