Faith, we have seen, is not a blind leap into the dark or a wishful thinking for things that we want to be true. Instead, faith is grounded in the objective work of God in history, His revelation in nature and in Scripture serving as evidence that what we believe is true. The Apostles never call us to believe in something without evidence; rather, the Apostolic preaching of the gospel always includes references to what the Lord has done for His people in the historical acts of Christ’s incarnation, ministry, death, resurrection, and ascension (Acts 2:14–36; Phil. 2:5–11).
Although the act of trusting the Messiah for salvation is something we do, we do not create faith in ourselves. Faith is God’s gift to His people (Eph. 2:8–10), the product of the living heart He gives in the new birth (John 3:1–8). If the Lord has changed our hearts, giving us the disposition to love Him, we will certainly exercise faith and persevere in it to the end (Phil. 1:6). But that we exercise faith at all is due to God’s sovereign grace. Born in Adam, we are disinclined to admit our sin and inability to save ourselves; we need the gift of faith to receive and rest on the Lord’s promises in Jesus. “With the heart one believes and is justified” (Rom. 10:10).
Theologians disagree as to whether the answer to question 21 of the Heidelberg Catechism makes our personal assurance of faith part of the essence of faith. We cannot settle that issue here, but let us note that the Westminster Confession says that believers may sometimes lack personal assurance (chap. 18). Much in Scripture supports the confession’s assertion that true Christians can sometimes doubt the authenticity of their faith. For example, the psalmist testifies to what many have called “the dark night of the soul,” a period of intense spiritual depression wherein we have significant doubts about the Lord’s presence and goodness (Ps. 88). But we are certainly not to assume that this writer was not a true believer even if he lacked full assurance at the time he wrote.
Prolonged periods of intense doubt should not be the norm of the Christian life, but assurance does develop and strengthen over time. Relying on fellowship, Bible study, the sacraments, and the other means of grace, we make our calling and election sure, increasing our assurance that we belong to Christ (2 Peter 1:10).
All of us will struggle with doubt at times, but that is not necessarily a sign that our faith is not genuine. When we have doubts, it is important to talk them over with those who are mature in the faith, so make sure that you have trusted friends and counselors with whom you can talk. Regular participation in corporate worship and our efforts to mortify our own sin will also help us grow in our assurance that we belong to Christ.