Some of us are wired to be extreme, always looking for boundary conditions, testing and exploring. We want to know our limits, how things work, and why things are the way they are. This can be a good thing, and it can also be problematic.
God tells us to let our moderation be known unto all men (Php 4:5a), relating this to the fact that He’s at hand, close by, imminently revealing Himself. (b) He evidently values stability, precision, an evenness of spirit that’s perfectly under our control, and would have this on constant display in us for all to inspect.
The word moderation is epieikes, also translated gentle (Tit 3:2), and patient (1Ti 3:3); it implies restraint on the passions, general soberness of living, being free from all excesses, fit or suitable, appropriate, mild. Perhaps the reference to the Lord’s ever-presence informs the choice of moderation here.
It’s not that we’re to avoid extremes altogether; indeed, we’re commanded to love God in the extreme (De 6:4) and rebuked for lukewarmness. (Re 3:16) We cannot love God too much, obey Him too well, or be too holy or righteous. (Mt 5:48)
The idea here is likely related to self-control, companied with a proper aim in our behavior. We’re to be constantly tuning the wavelengths of our expression to align perfectly with God in every situation. This is the very definition of being appropriate, and it requires both discipline and holy intention. (Php 3:15-16)
Controlling ourselves apart from a godward focus leads to pride and will-worship (Col 2:23), and a godward focus without self-control is spineless passion. (Pr 25:28) Neither are Christ. (Ep 4:20)
We’re to both approve things that are excellent (Php 1:10) and also master ourselves in pursuing them. (1Co 9:27)
Yet our perception of excellence is incomplete (1Co 8:2), and our aim depends on what we can currently apprehend. (Php 3:13-14) As we pursue our present vision of Christ He reveals more of Himself to us (2Pe 3:18), and then we find that our definition of perfection is refined and we adjust.
Spiritual life is a cycle of moderating ourselves in Christ, for Christ, adding to our faith, being sanctified and transformed into His image. (Ro 8:29)