What does James 1:8 mean?

This verse completes a crucial idea which James introduced in verse 5. God promises wisdom to all who ask Him for it. He promises to give it generously and not based on our merit. The caveat is that we must believe and not doubt. We must not seek wisdom from sources contrary to God at the same time, expecting to weigh God's wisdom against others and decide which we will follow. We can consult godly advisors, and look to God's creation, but we can't weigh His wisdom against that of the world before we decide who to trust.

Verse 7 made it clear that a doubtful person—the one who treats God as only one of many options—should not expect to receive any wisdom from God. This verse calls that person both double-minded and unstable. Trying to live by God's wisdom while also following a form of "wisdom" from another source will always lead us in two different directions. We will always be deciding whose wisdom feels more right to us in any given moment. In that way, we end up making a god of our own ability to pick the "right" wisdom from day to day.

James makes it clear that the only stable life is one in which a believer has resolved to follow God's wisdom—period. Those who trust the Father seek wisdom from the Father and follow the wisdom the Father gives, no matter what.