I love the first question and answer from the Heidelberg Catechism, written soon after the Reformation. It succinctly explains a Christian’s hope and basis for assurance:
Q: What is your only comfort in life and death?
A: That I am not my own, but belong–body and soul, in life and in death — to my faithful Saviour Jesus Christ. He has fully paid for all my sins with his precious blood, and has set me free from the tyranny of the devil. He also watches over me in such a way that not a hair can fall from my head without the will of my Father in heaven: in fact, all things must work together for my salvation. Because I belong to him, Christ, by his Holy Spirit, assures me of eternal life and makes me wholeheartedly willing and ready from now on to live for him.