But the Lord is faithful, who will establish you, and guard you from the evil one.
Paul is here stating that the safety of the believers in Thessalonica is insured by the Lord’s fidelity, although it requires their own obedience unto the Lord and Paul had unshakable faith that they WOULD BE obedient. A faithful Lord watching over faithful believers will win an assured victory over Satan, regardless of his schemes or power (Green 293).