My brethren - a phrase often found in James, marking community of nation and of faith.
all joy - cause for the highest joy [Grotius]. Nothing but joy [Piscator]. Count all “divers temptations” to be each matter of joy [Bengel].
fall into - unexpectedly, so as to be encompassed by them (so the original Greek).
temptations - not in the limited sense of allurements to sin, but trials or distresses of any kind which test and purify the Christian character. Compare “tempt,” that is, try, Gen 22:1. Some of those to whom James writes were “sick,” or otherwise “afflicted” (Jam 5:13). Every possible trial to the child of God is a masterpiece of strategy of the Captain of his salvation for his good.