Let the lowly brother boast in his exaltation, and the rich in his humiliation…
—James 1:9–10a

James’ two commands in this passage “rhyme” with his first command: “Count it all joy, my brothers, when you meet trials of various kinds.” The “rhyme” becomes more apparent to your ears as you acclimate to this “heavenly language,” but for now, this much should be clear, all of these commands are for brothers, all are odd, and all of them concern joy.
The word you have as “boast” in v. 9 is the same word translated “rejoice” in Romans 5:3; a text which proves especially significant in linking all these commands together. “[W]e rejoice [boast] in hope of the glory of God. Not only that, but we rejoice [boast] in our sufferings, knowing that suffering produces endurance.” Christian brothers are commanded rejoice in their trials. Those who are lowly are commanded to rejoice in their exaltation and those who are rich are commanded to rejoice in their humiliation. All commands for brothers. All odd commands. All commands to rejoice.
But “rejoice” doesn’t quite capture the fullness of this word. It does have the sense of boasting or glorying. To get some idea of what James calls on us to do here, lets observe Paul doing it in Philippians 3:3–11. What Paul says there doesn’t directly concern poverty and riches, but I believe you will be able to hear again the same “rhyme” in Paul as we have here in James.
“For we are the circumcision, who worship by the Spirit of God and glory [boast, rejoice] in Christ Jesus and put no confidence [i.e. we don’t boast or glory] in the flesh— though I myself have reason for confidence in the flesh also. If anyone else thinks he has reason for confidence in the flesh, I have more: circumcised on the eighth day, of the people of Israel, of the tribe of Benjamin, a Hebrew of Hebrews; as to the law, a Pharisee; as to zeal, a persecutor of the church; as to righteousness under the law, blameless. But whatever gain I had, I counted [a similar kind of accounting as that presented in James 1:1] as loss for the sake of Christ. Indeed, I count everything as loss because of the surpassing worth of knowing Christ Jesus my Lord. For his sake I have suffered the loss of all things and count them as rubbish, in order that I may gain Christ and be found in him, not having a righteousness of my own that comes from the law, but that which comes through faith in Christ, the righteousness from God that depends on faith— that I may know him and the power of his resurrection [exaltation], and may share his sufferings, becoming like him in his death [humiliation], that by any means possible I may attain the resurrection from the dead.”
Do you see Paul, your brother in the Lord, both boasting in his exaltation and in his humiliation? This is the odd, peculiar kind of boasting James is calling us to here, whether we be rich or poor in this life. What Paul does helps you see the single essence that underlies both of these commands in James. That something singular does indeed underlie both boastings is also evident when Paul speaks of the wisdom that trials have taught him in Philippians 4:11–13.
“Not that I am speaking of being in need, for I have learned in whatever situation I am to be content. I know how to be brought low, and I know how to abound. In any and every circumstance, I have learned the secret of facing plenty and hunger, abundance and need. I can do all things through him who strengthens me.”
A singular secret underlies meeting both situations with contentment. What is this singular foundation? One’s union with Christ. The poor, in particular, are to glory in their unity with Christ in His exaltation, while the rich, in particular, are to glory in their unity with Christ in His humiliation. If the poor share in Christ’s exultation in heaven, the rich share in Christ’s humiliation on earth.
There is a singular, foundational, fundamental reality behind both of these boastings.
“Thus says the LORD: ‘Let not the wise man boast in his wisdom, let not the mighty man boast in his might, let not the rich man boast in his riches, but let him who boasts boast in this, that he understands and knows me, that I am the LORD who practices steadfast love, justice, and righteousness in the earth. For in these things I delight, declares the LORD’” (Jeremiah 9:23–24).
How is it that we come to know Yahweh who practices steadfast love, justice, and righteousness in the earth? Supremely, it is through the cross of Christ. “But far be it from me to boast except in the cross of our Lord Jesus Christ, by the world has been crucified to me, and I to the world” (Galatians 6:14). Here, the poor are being called on to boast in the riches gained by the cross of Christ and the rich are called on to boast in their sharing in the humiliation of the cross of Christ. Fundamentally, both are called on to rejoice in Christ—the Christ who humbled Himself on earth and who is now exalted in heaven.