It means that we trust him. When we have faith in Jesus Christ, it means more than simply believing that he exists, more than believing that he is the Son of God, more than believing that he died for our sins. Those are true, and they are essential, but faith also means trusting him day by day, walking with him, knowing that the love he has for us will never fail. We can have confidence in him. Paul described salvation as a reconciliation between God and his people.
Reconciliation is also a relationship word.
This means that we are now his friends rather than his enemies. This personal reconciliation is important to us. By becoming friends of God, we also become friends of each other. Since we will each live with God eternally, we will also live with one another eternally, in a relationship characterized by love. We are reconciled not only with God, but also with each other.