Paul speaks for himself and also for Silas and Timothy. They had all preached among the Thessalonians.
There may be those think that they are Christian, that they walk with Christ, that they have been saved. Are there evidences? Perhaps you are still outside the kingdom, perhaps you are still lost, perhaps you are still under judgement, perhaps you have been deluded and it is a great mistake. The kindest thing we can do is to point out the evidence for this, for while there is life there is still opportunity to seek the Lord.