‘And we have confidence in the Lord with regard to you that you both do and will do the things which we command.'
Confident that the Lord will establish and guard them he also has confidence that they are fulfilling and will fulfil what he and his companions ask of them. Whether ‘in the Lord' refers to ‘having confidence in the Lord' that He will be the source of their obedience, or is ‘with regard to you in the Lord', referring to the sphere in which they will be obedient, is an open question but the general idea is the same, confidence in the Thessalonians because of the Lord's activity. ‘The things which we command' probably refers to the commands which are about to follow.