Romans 15:13 — Now the God of hope fill you with all joy and peace in believing, that ye may abound in hope, through the power of the Holy Ghost.
God is the author of hope — assurance
Should read God of the hope.
This is Paul's final reason for unity — we share the hope.
Trinity: God authored the hope, Christ embodied the hope, the Holy Spirit empowers us to embrace it.
This verse is a great summary of the blessed life in the brotherhood formed by our oneness in Jesus Christ. The source of that life is the God of hope. The measure of that life is that we shall be filled "with all joy and peace." The quality of that life is joy and peace which He desires for us. The condition of that life is faith — we enter by believing. The purpose of that life is that we might abound. The enabling of that life is divine power. And the director of that life is the Holy Spriit. These seven aspects sum up the Christian life. — Donald Grey Barnhouse, God's Glory, page 72-73.