Why does God accept our offerings?
Christ does not require offerings (words and actions) from us to be the means for Him to shower the world with graces. Since nothing is impossible for God, Christ accepts our offerings not for His benefit, but for our own. To illustrate my point, consider the following analogy:
A dad is mowing the lawn with a gas powered push mower. His young 4 year old son sees him working and wants to help. The dad sees the great enthusiasm in his son and allows him to help. The dad places his son's hand on one of the handlebars and tells him to push. The young boy is full of excitement as he pushes hard on the handlebars, believing that he is helping his dad mow the lawn. When the chore is done, the dad complements his son for the help, and tells his son that he can help whenever he wants to. The boy leaves in excitement, and tells everybody enthusiastically that he got to help his dad.
As we adults are aware, the dad in this story is not benefiting from his son's assistance. The dad is the one who is physically mowing the lawn, not the boy, because the boy is physically too weak to mow the lawn. The dad is allowing his son to help, so that the boy can learn the value of hard work.
With God, the same is true. Like the dad in the story, God is the one who is actually doing the work (sanctifying the world), not us. God allows His children to help Him by accepting their offerings not for His benefit, but for their own spiritual growth.