Main point summary
Rejoice during trials, since God works through them to produce endurance and make you complete.
e Count it all joy, my brothers, 1
Rejoice, brothers and sisters,
when you meet trials f of various kinds,
WHEN you encounter trials of which there will be many types,
for you know
BECAUSE you know something
that g the testing of your faith h produces steadfastness.
PARTICULARLY that the testing of your faith [through these trials] cultivates endurance.
And let steadfastness have its full effect,
THEREFORE let this endurance mature in trials,
that you may be i perfect and complete,
IN ORDER THAT you may be whole and complete in Christ,
lacking in nothing.
THAT IS being deficient in nothing in displaying the image of Christ.
"When" indicates a certainty of meeting this faith testing trials, else James could have used a conditional such as "if".
These trials aren't meaningless. Rather, through these trials our faith is tested which yields endurance.
The purpose for which we allow this endurance to grow is to become more like Christ!
Rejoice in your trials fellow Christians! Though not solely trials of persecution (though these are the primary stimulus of the writing) but "trials of various kinds". So, when because of your faith your friends belittle you, your family ignores you and your teachers dismiss you or illness strikes you and tragedy collides with loved ones or burdens of a job tax you, consider it full of joy. Your response is not to be stoic, nor ignore the pain, nor live in self pity, but to be full of joy. Why? It's not for the experience alone, but we consider it joy because this testing of your faith produces endurance. It is not a test solely for the sake of "testing", namely to solely see whether or not your faith is genuine causing much angst asking "Will I pass the test?" like a school student might experience. This testing actually has another role, to produce endurance, which itself is not the end goal. The end goal of these trials is that we would grow in Christ! Consequently, rejoice in these trials since through them God shapes you to be mature in Christ.