18 If possible, so far as it depends on you, live peaceably with all.
Paul here presented a double qualification for living in harmony with others, because doing that might not always be possible.
18 If possible,
It is not possible to live peacefully with everyone. There are some knuckleheads who will not reconcile with others. There is a limit to the challenge here.
so far as it depends on you,
Since there are people with whom we cannot live peacefully, we need to make sure that we are not the cause of the problem. The onus rests upon the Christian to take initiative in reconciliation. This requires self-examination.
live peaceably with all.
Peacemaking is a biblical priority. Any ministry, whether it is a church or a parachurch organization, must have harmony for their ministries to be most effective.
Harmony among believers is a priority of God.
Some Christians have an unrealistic ideal that they can resolve problems with anyone no matter how unreasonable they may be. The truth is that there are those who will not be reconciled. We have no control over the will of others.
God never asks the believer to seek peace at the cost of truth. That would be an unworthy accommodation to something other than biblical principles.
Peacemaking is a biblical priority:
Mt 5:9, Blessed are the peacemakers, For they shall be called sons of God.
He 12:14, Pursue peace with all people, and holiness, without which no one will see the Lord:
Jas 3:17, But the wisdom that is from above is first pure, then peaceable, gentle, willing to yield, full of mercy and good fruits, without partiality and without hypocrisy.