While this may sound somewhat sacrilegious, I think the stock market is a pretty good analogy for one's walk with God. Let us take the Sraits Times Index (STI) as our case in point and assume that how well our life is going is equivalent to the closing price of the STI each day.
For anyone just starting out at trading equities, or the more risky warrants, you know that emotions play a big part in determining where prices will be each day. Stock market guidebooks and gurus often talk about the 2 biggest hurdles that every investor needs to keep in check, namely fear and greed. But often times one cannot help but feel the pinch when a one-day correction wipes out over 5% of your investment (as on 28 Feb 2007).
In the same way, we occasionally face obstacles in life that appear so big that we just feel like throwing in the towel. Whether it's our relationships, or our work, or our spiritual walk, we get coaxed into thinking that all is lost. So we give up, cut our losses and swear never to use our hard-earned money to buy the STI ETF ever again.
However, had we taken a longer term view of the STI over the past 5 years, we see that the upward trend is undeniable, and Feb 07 was just a drop in the ocean. That's comforting for long-term investors, though not very useful info for the short-term punters. But our relationship with God is not meant to be a hit and run. When we said the Sinner's Prayer, we were signing up for the long-term.

The problem is that we don't have the benefit of nice on-line charts to remind us of God's plan for our lives. And that's where journalling comes in. I will be the first to admit that it requires quite a bit of discipline to do, but the benefits are well worth it. As you recall the times when you thought all was lost, we see the hand of God reaching down and plucking you out from the depths of despair.
So we derive our confidence in God from past experience (historical trends) as well as good fundamental knowledge. Looking at the chart below, the STI looks a lot less friendly if we take a super long-term view. So it's ok to sell, but we need to do so for the right reasons.

How do we get insight into the fundamentals? With shares, we look at all the wonderful ratios out there, like P/E, ROE, ROA, P/B, etc. With our spiritual lives, it's all about prayer and reading the Bible, i.e. getting in touch with the most important insider of them all.
Claiming to be a Christian and not praying regularly is kind've like buying a stock and not reading the company's annual report -- you don't really know what's going on and are just hoping for the best. It's no wonder that when 28 Feb 07 hits, you panic and liquidate your holdings, only to regret just 2 months later.
I think some of the ideas may not map very well to the STI analogy, but I hope you get the point :) For avoidance of doubt, this is not an inducement to buy the STI :P