Where does assurance come from? His Spirit confirms with our spirit that we are the children of God.
Here are some excellent Biblical truths to help confirm this.
We can test ourselves to see if we are in the faith by reminding ourselves, often, of what John says in his epistle. Follow through from the first chapter which I’ve linked.
I wrote these things to stir us all up, after this sermon began, which I’m currently watching:
I pray we are all truly inspired to hold firm to the faith, once delivered to the saints.