v1: Teachers and leaders have extra responsibility (Heb 13.17), and are accountable (Rom 2.17-23). A godly example is therefore essential. Each leader must set and maintain a high godly example.
v2: We all stumble, and James does not exalt himself over others. Stumbling is not something deliberate, but rather carelessness or rashness; we fall short. Our best endeavours are imperfect.
Our words reflect our spiritual state; a bridled tongue is a mark of spiritual maturity, see 1.26; Prov 10.17; Luke 6.45. See Christ's own example, Luke 4.22; John 7.46.
v3-8: The power of the tongue. We are very likely to stumble in word, and by that others are harmed. To be able to control the tongue gives us power over the whole body (illustrated in v3-4); the horse is driven by a force within, the ship by a force outside; and each can be driven by something small; we can therefore know victory over both types of problem and temptation.
The tongue is a mighty power for evil. Whilst no man can tame the tongue, all things are possible with God; and Christ's words brought eternal life (John 6.68). The tongue, James says, is a fire. (It is not like a fire, but is a fire!) It sets the whole created world ablaze, such is its power. The reference to the "whole body" may be taken to refer to a local church.
Our own weakness should encourage prayer (Ps 141.3).
v9-12: The problem of inconsistency; our words should be both consistent and constructive, see Is 53.9. In particular, we are not to curse men.
A mixture of sweet and bitter will taste bitter; a small amount of bad words can pollute an otherwise blameless life.
v13: A new section, to 5.18; the nature of true wisdom; how we should live. This starts with a good conscience and good works, vital characteristics of true wisdom. Again, this was a challenge to those who claimed to be something, but who lacked evidence.
The humility (or meekness) of wisdom; an attitude of heart that accepts God's will without dispute or resistance.
v14-16: The way of man; bitter envy and self-seeking; the result is disorder and every evil practice. The wisdom of the world is therefore very different from true, heavenly wisdom. James is clear; worldly wisdom does not descend from above, and these things actually oppose the truth.
The use of the pronoun "you" implies that James had observed these attitudes within the churches. His words are not some empty theorising, but a direct application to a current situation.
v17: True wisdom is spiritual;
Pure, chaste, holy; free from defilement;
Considerate, peace-loving, peaceable; seeking union and communion, avoiding offence;
Submissive, willing to yield; compliant, ready to obey; not seeking one's own rights, or even preferences;
Full of mercy; practical meeting of the needs of others;
Good fruit; beneficial in character and in effect.
Such things cannot be engineered by man; we need God's help and power to live this way.
v18: The fruit of righteousness, brining peace into the lives of others.