In this closing passage, the writer requests his readers to pray for him. Indeed, prayer is not an optional extra or something to do as a last resort and is a recognition of the fact that we are needy people. Indeed, whatever our situation, we all need the Lord's help. We are, after all, not robots but flesh and blood, and are subject to frailty.
The writer of the Book of Hebrews believes prayer works, and it works because God is at work. We are encouraged to pray, with sincerity and with heart and soul. God, working, to make us more obedient, conforming us to His will. It is a great work that the Lord is about to make us more like HIs Son, who is the glorious main theme of this entire book.