Of all the Reformation-era catechisms, perhaps none is as well-loved as the Heidelberg Catechism. In the opening question and answer, the personal and distinctive tone of the catechism becomes evident. "What is your only comfort in life and in death?" This is not a theoretical question—"What would be necessary if God were to comfort sinners?" Rather, this is a very practical question—"How do I have comfort as long as I live and then when I die?"
The key word in the opening question is comfort (German, trost). The word refers to our assurance and confidence in the finished work of Christ. This comfort extends to all of life and even to the hour of death. As one of the authors of the catechism (Zacharius Ursinus) puts it in his commentary on the catechism, this comfort entails "the assurance of the free remission of sin, and of reconciliation with God by and on account of Christ, and a certain expectation of eternal life; impressed upon the heart by the Holy Spirit through the gospel, so that we have no doubt but that we are saved forever, according to the declaration of the apostle Paul: Who shall separate us from the love of Christ?" Note that the catechism speaks of our "only" comfort. There is no other such comfort and assurance to be found apart from Christ.
In answering the opening question, the catechism asserts that "I, with body and soul, both in life and in death," will have this comfort. A paraphrase of Romans 14:7–8 here, we are reminded that God’s care extends to us throughout the course of our lives. Christ has removed the curse; there is assurance of salvation in this life and the resurrection of our bodies at the end of the age (see Q & A 57–58). This knowledge comforts us now and prepares us for whatever lies ahead.
Our comfort derives from the fact that "I am not my own." These words are taken from 1 Corinthians 6:19–20: "You are not your own, for you were bought with a price. So glorify God in your body." We are Christ's, and He will do with us as He wills. This comfort is based on the fact that God is sovereign and has the power to do as He has promised.
This wonderful fact is further spelled out in the next part of the answer. "But [I] belong to my faithful Savior Jesus Christ." The catechism directs us away from our faith (the subjective) to Christ's obedience—my "faithful" Savior (the objective). Christ fulfilled all righteousness and died for our sin upon the cross for me. The specifics of Christ's obedience are spelled out in more detail in the next part of the answer: "who with His precious blood." These words come from 1 Peter 1:18–19: ". . . knowing that you were ransomed from the futile ways inherited from your forefathers, not with perishable things such as silver or gold, but with the precious blood of Christ, like that of a lamb without blemish or spot." The death of Christ is the only means by which the guilt of human sin can be removed (expiation) and the wrath of God turned aside (propitiation). The catechism reminds us that the ground of our salvation is the work of Christ for us, not our faith or our own good works.
Next, the first answer of the catechism tells us that the death of Jesus lies at the heart of this promised salvation because He "has fully satisfied for all my sins." Christ's death alone satisfies the justice of the holy God (Rom. 3:21–26). No human work or religious ceremony can do this. Not only that, but His death has "redeemed me from all the power of the devil." This is an echo from 1 John 3:8: "The reason the Son of God appeared was to destroy the works of the devil." Satan has been cast out of heaven so that he can no longer accuse us before the heavenly court. Christ's victory over him is evident at the cross (Col. 2:13–15).
The catechism then states the precious truth that our assurance of salvation and our perseverance in faith are also the work of Christ. "[Christ] so preserves me that without the will of my Father in heaven not a hair can fall from my head." This is taken from Matthew 10:29–30: "Are not two sparrows sold for a penny? And not one of them will fall to the ground apart from your Father. But even the hairs of your head are all numbered." To possess the comfort promised in the Gospel, I need to know that God’s sovereign care extends to all aspects of my life. Nothing happens to me apart from the will of God. In fact, "all things must work together for my salvation" (see Rom. 8:28). God has ordained all things. He redeems us from sin. And in the end, God will turn it to my good.
Finally, we learn that this comfort becomes mine through the work of the Holy Spirit. "Wherefore, by His Holy Spirit, He also assures me of eternal life." The Holy Spirit bears witness to the truth of God's Word and confirms the promise God made to me that He will save all those who trust in Christ. This same indwelling Spirit "makes me heartily willing and ready from now on to live unto Him." It is God who will see His good work through to the end. That one who justifies me will also sanctify me. He who began a good work in me will see it through to the end.