In our church membership document, the word assurance comes a number of times. Here are some of the pertinent sections on how the church helps with our assurance.
Jesus said, ‘if you love me, you will keep my commandments… whoever has my commandments and keeps them, he it is that loves me’ (Joh 14:15, 21a). Similarly, James asks, ‘what good is it, my brothers, if someone says he has faith but does not have works? Can that faith save him?’ (James 2:14). It’s all too easy to convince ourselves that we’re saved because we ‘made a commitment’ or said the ‘sinner’s prayer’, but scripture warns us about deluding ourselves into thinking we’re saved when we are not. We know we belong to Christ when we obey him and love his commandments (1Jo 5:3).
When we join a church, we are asking the membership to hold us accountable to what we claim to believe. We ask members to encourage us in the faith and challenge us whenever we drift away from obedience to Christ. Joining a church in membership is an act of obedience that lets others commit to us in our Christian walk so that we can be sure our salvation is genuine.
A second section reads this way:
Membership is the church’s affirmation that somebody is a true Christian (Mat 16:19; 18:18). The church looks at somebody’s life, hears their explanation of the gospel and how they came to believe it, and tells that person to join the family. Whilst membership doesn’t guarantee somebody is a Christian, it is a further affirmation of genuine belief. As we submit to church discipline and strive to live holy lives, other members see our desire to be more Christlike and can affirm our faith. Church membership deepens our assurance.
Here, in a similar vein, is Mark Dever: