'Sure' in the Bible

This is how we can be sure that we have come to know him: if we continually keep his commandments.

But whoever continually keeps his commandments is the kind of person in whom God's love has truly been perfected. This is how we can be sure that we are in union with God:

The person who keeps his commandments abides in God, and God abides in him. This is how we can be sure that he remains in us: he has given us his Spirit.

And if we know that he listens to our requests, we can be sure that we have what we ask him for.