There are three important aspects to this instruction. First, we are to be "moderate," the core meaning of which is to be equitable or fair, with further associations of mild and gentle.
The Greek word rarely appears in the New Testament. Twice the qualifications of church leaders include this characteristic (1 Timothy 3:3 and Titus 3:2), both times stressing the "gentle" aspect of the term. Once, and importantly, the term is used in a broad sweep of adjectives outlining the "wisdom that is from above" (James 3:17)--all aspects, incidentally, fleshing out the idea of "fair" or "equitable."
Secondly, today's verse tells us to make our moderation "known unto all men." That is demanding, since it is more difficult to apply equity to all people rather than just attempt to be fair and gentle in our dealings. Surely the Holy Spirit is insisting that our inner character be "moderate," so that the resulting actions will flow from a person's character rather than his circumstance. As noted of those of the Corinthian church, they were "manifestly declared to be the epistle of Christ" (2 Corinthians 3:3). Everybody "reads" us, and what others decide about us must include the reputation of fair and gentle behavior to all.
Finally, the reason that this requirement is so significant is because "the Lord is at hand." Although a quick application might lead one to think, "The Lord is coming back soon," the time element is not at all implied in the sentence. A better translation may be "the Lord is alongside," "he is close," or even "the Lord is with you." It is easy, sometimes, to forget that God indwells us through the Holy Spirit and that our every action and thought are known by our Creator (Psalm 139:3-4). HMM III