‘For now we live if you stand firm in the Lord.'
‘Now we are alive.' This use of the word live emphasises the great burden under which Paul had suffered. He had felt dead and discouraged, but now he had sprung to life. We tend to overlook the dreadful burdens he had to bear, the constant worries as more and more seemingly bad news filtered through which could not be tested, the pressures of learning of the activities of false teachers, especially when they were accompanied by seeming success, the constant brushes with authority and what they could mean for the success of his mission. But now this great news had come though that this vital church was alive and well and prospering. The word was going out in Macedonia and around. All was well.
Note that ‘if' (ean) is followed, not by the subjunctive of doubt, but by the indicative of greater certainty. Possibly we should paraphrase ‘as long as you go on standing firm'. For the meaning of the verb compare 1 Corinthians 16:13; Galatians 5:1; Philippians 4:1.