As Christians, we are to be caring for one another. We are all in a battle with the world, the flesh and the devil. And there are times when Christians fall into deliverate sin. Trespasses are serious sins. Paul is talking to Christians here. He says, "Brethren, …". This should make it pretty clear that it is possible for Christians to sin seriously (most of us realise that, but there are extreme positions which claim sinlessness is normal for Christians).