Some seem to think that the gospel is relevant only at the point that a person becomes a follower of Christ.  After that, the work of Christ in saving sinners can be safely left behind, and we can move on to other matters.

Not so, argues Derek Thomas.

Consider:

In Rom 1:15, Paul expresses his eagerness to preach the gospel to those who are already believers.

In Rom 16:25 the apostle asserts that the gospel is able to strengthen those same believers.

In 1 Cor 15:1 he wishes to remind his readers of the gospel.

In Gal 1:6-7 he warns of the danger of turning to a different gospel.

Christians need the gospel:

1. to heal a condemning conscience.  The apostle John recognises that a troubled conscience can get in the way of assurance of salvation; his remedy is to apply the gospel (1 Jn 3:19f).
2. to prevent the onset of legalism.  Legalism insists on obedience to laws that are not laid down in Scripture, or on obeying laws that are mandated in Scripture for reasons other than sheer gratitude for God’s grace.  Paul counters the claim that circumcision was necessary by a healthy dose of gospel truth (Gal 3:1-4).
3. to deflate our pride.  The gospel teaches us that we bring nothing to the table, except our need.  And we need that same gospel arm us in battle against pride, and to nurture a true spirit of humility.
4. to enable us to live a life filled with joy.  The gospel brings joy (Lk 2:10).  We are urged to rejoice in the Lord always (Phil 4:4).  Joy is a fruit of the Spirit (Gal 5:22).