One of the characteristics of God is that He is faithful.  Though everyone around us may fail us God remains faithful.  He always keeps His promises and is always a present help.  We are reminded in this passage that despite the struggles and persecution of the Thessalonian church the Lord faithfully would provide for them.  The Lord would give them strength for their needs and to deal with the devil.  We may have confidence in the Lord who faithfully went to the cross and took our sin and that we might respond in turn with obedience and a faithful heart.