Adam Clarke on Romans 12:18

If it be possible - To live in a state of peace with one's neighbors, friends, and even family, is often very difficult. But the man who loves God must labor after this, for it is indispensably necessary even for his own sake. A man cannot have broils and misunderstandings with others, without having his own peace very materially disturbed: he must, to be happy, be at peace with all men, whether they will be at peace with him or not. The apostle knew that it would be difficult to get into and maintain such a state of peace, and this his own words amply prove: And if it be possible, as much as lieth in you, live peaceably. Though it be but barely possible, labor after it.