Here’s the KJV (click link for NIV)
6 But let him ask in faith, nothing wavering. For he that wavereth is like a wave of the sea driven with the wind and tossed. 7 For let not that man think that he shall receive any thing of the Lord. 8 A double minded man is unstable in all his ways.
I actually prefer the KJV to the NIV (and most modern translations) for this section at least. This is first major mention of faith in the book of James. As we will see, faith is not just believing (“without doubt” as most modern translations put it), but has to do more with being faithful, and so not wavering. Like wisdom (verse 5) is not just mental, but practical (doing the right thing), so it is with faith. One can be faithful and have doubts. It has to do with an entire disposition. Let’s take an example of a married couple. Because I’m a guy, I’ll take it from the man’s perspective (but it works either way). Which is better: a man who believes without question that his wife loves him unconditionally and uses this as a license to cheat on her, neglect her and do whatever else he selfishly wants (on occasion); OR a man who (on occasion) has some doubts about how whether or not his wife loves him without question yet, regardless of this, is wholly faithful to her out of his love? Which one is better? The one who wavers in devotion, but knows intellectually he’s ok, or the one who is completely faithful, with or without doubts? Now, clearly it is better to have both, but if we stick with one, which is better. This idea of faith will come up again.
James is saying our relationship should be like that of a faithful person. Someone who does not waver depending on the situation in our devotion. If we do, how can we claim to be a follower of Christ? If we are brazenly and openly sinning or denying Christ anytime the winds change (that’s pretty unstable), how can we expect God to give us whatever we ask for, simply because we know he’s good? Of course he’s good, that’s why he won’t give it. For starters, you don’t seem to really care about getting wisdom (if you are so two-faced). And second, you won’t ever learn how to be faithful. This is a call to be faithful servants, not ones who change daily (and are thus unstable).
How faithful are you? Does it help to be reminded that Jesus Christ is our faithfulness? (See 2 Timothy 2:11-13)