But the one who is rich should take pride in his low position, because he will pass away like a wild flower.
I had to do a little digging on this one.
In verse 9, remember that it was talking about a brother in humble circumstances. The word humble or low is the Greek word tapeinos, which is an adjective. So, the circumstances are low or humble, and the boasting that he does is literally in his height.
The rich man is to also boast, but notice that his boasting isn't in his height, it is in his low position. That low position, in the original, is just one word; it is the word, tapeinosis. Look familiar? That is the noun form of the adjective that is describing the other man's circumstances. The rich man's boasting is when he is knows that ultimately he shares the same fate as the man who does not have. If a rich man can come in humility to Christ, there is a glory in that.
By the way, I was studying the roots of the word that is translates as glory in this and the last verse. Study light tells me that it is a combination of two words, one that means "to boast" and the other that means "to pray". I am putting this in here just in case you might think that I am promoting boasting. In these verses the boasting, glorying, or taking pride is not in the sinful sense, as they can be sometimes. They are truly directed to God and for God. The heights that the poor man reaches are the heights in Christ and the humility of the rich man comes from a work of Christ in that man's heart, just like all humility is.
So ultimately we boast of Christ! We boast of who He is and what He does!