He decided to die, why groan under the fire?

He was brilliant,
he was hardworking,
he was strong

"was" "was", that's what they used for him. Even while he groaned.

This part is really quite brilliant, very aware.

I do not understand the last line though : "bring depression captive, into the obedience of Jesus Christ."

I don't think Jesus wanted us to take people too him as captives, maybe you mean differently than I understand.