Let him seek peace It is not enough to embrace it when offered to us, but it ought to be followed when it seems to flee from us. It also often happens, that when we seek it as much as we can, others will not grant it to us. On account of these difficulties and hindrances, he bids us to seek and pursue it.

Let him eschew evil - Let him avoid all evil. Compare Job 1:1.
And do good - In any and every way; by endeavoring to promote the happiness of all. Compare the notes at Galatians 6:10.
Let him seek peace, and ensue it - Follow it; that is, practice it. See the Matthew 5:9 note; Romans 12:18 note. The meaning is, that a peaceful spirit will contribute to length of days:
(1) A peaceful spirit - a calm, serene, and equal temper of mind - is favorable to health, avoiding those corroding and distracting passions which do so much to wear out the physical energies of the frame; and,
(2) such a spirit will preserve us from those contentions and strifes to which so many owe their death. Let anyone reflect on the numbers that are killed in duels, in battles, and in brawls, and he will have no difficulty in seeing how a peace fill spirit will contribute to length of days.

Let him eschew evil,.... Avoid all kinds of evil, hate it, abstain from the appearance of it, and have no fellowship with it; and particularly should avoid rendering evil for evil, or taking revenge on persons for doing him ill:
and do good; everything that is good, all good works, according to the will of God, in the exercise of faith, from a principle of love, and with a view to the glory of God; and without trusting to them, and depending upon them for life and salvation; and particularly do good for evil; do good to all men, acts of kindness and beneficence, even to enemies, and especially to them that are of the household of faith. The Jewish interpreters (w) on the psalm from whence these words are taken observe, that in the first of these clauses are contained all the negative precepts, whose number with them is three hundred, sixty, and five; and in the latter of them, all the affirmative precepts, which amount to two hundred and forty eight:
let him seek peace and ensue it: "or pursue it"; let him seek after it, in the world, and with all men, as much as possible, yea, with his very enemies; and live a peaceable and quiet life, in the kingdom, city, town, and neighbourhood where he is; and particularly in the church of God, and with the saints; which he should seek with all diligence and eagerness, and pursue with all rigour to the utmost of his power; and endeavour to cultivate all he can, and follow the things which make for it. The note of one of the Jewish commentators (x) on this passage is, "seek peace", in thine own place; "and pursue it", in another place,
(w) Aben Ezra & Kimchi in Psal. xxxiv. 14. (x) Jarchi.

In oldest manuscripts, Greek, "Moreover (besides his words, in acts), let him."
eschew--"turn from."
ensue--pursue as a thing hard to attain, and that flees from one in this troublesome world.

Let him seek - To live peaceably with all men. And pursue it - Even when it seems to flee from him.