The word you ask about in James 4:6 is ἀντιτάσσεται (antitassetai) which is from "anti" and the middle voice of "tasso"; to range oneself against, i.e. Oppose. BDAG suggests the following for the root verb ἀντιτάσσω (antitassó):
- oppose, resist, eg, Acts 18:6, Rom 13:2, James 4:6, 5:6, 1 Peter 5:5.
James 4:6 is a quote from Prov 3:34 in the LXX. See also 1 Peter 5:5 which also quotes the same OT verse. Matthew Poole observes:
God resisteth; it is a military term: God sets himself, as in battle,
against the proud, defying, beating down, exposing to contempt, and
destroying them; he is so far from giving them more gifts, that he
rather spoils them, as sworn enemies, of what they have.
This resistance of pride he shows not only in the explicit
declarations of his word, but in the arrangements of his providence
and grace: (1) In his providence, in the reverses and disappointments
which occur; in the necessity of abandoning the splendid mansion which
we had built, or in disappointing us in some favorite plan by which
our pride was to be nurtured and gratified. (2) in sickness, taking
away the beauty and strength on which we had so much valued ourselves,
and bring us to the sad condition of a sick bed. (3) in the grave,
bringing us down to corruption and worms. Why should one be proud who
will soon become so offensive to his best friends that they will
gladly hide him in the grave? (4) in the plan of salvation he opposes
our pride. Not a feature of that plan is fitted to foster pride, but
all is adapted to make us humble.
That is, God always tries to remind us of our great need of Him without ever forcing us to serve and love Him. Forced love is not love at all! We are reminded of these truths in the same verse of James (never should the first part of the verse be separated from the second part); But he gives us more grace. That is why Scripture says: "God opposes the proud but shows favor to the humble."
As humble (needy) servants of God we need His strength and grace constantly. The proud cannot receive God's grace because they feel no need, so God attempts to remind the proud as this text so succinctly attests.