"What is your only comfort in life and death?"
The answer is: "That I am not my own, but belong--body and soul, in life and in death, to my faithful Savior 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 whole-heartedly willing and ready from now on to live for him."
The opening question and answer is from the Heidelberg Catechism.You can read the catechism here.
If you're new to reformed theology, you can click here to read and see what it's all about. Personally, I think the video below (part 1 of a totally free series called, "what is reformed theology") will give you a solid overview of reformed theology, but the other link is a good place to go as well.
Entire Heidelberg Catechism
What is reformed theology video series (free to watch online)
Counted righteous in Christ