en_tn/rev/10/05.md

raised his right hand to heaven

He did this to show that he was swearing by God. (See: rc://en/ta/man/translate/translate-symaction)

He swore by the one who lives forever and ever

"He asked that what he was going to say would be confirmed by the one who lives forever and ever"

the one who lives forever and ever

Here "the one" refers to God.

There will be no more delay

"There will be no more waiting" or "God will not delay"

the mystery of God will be accomplished

This can be stated in active form. AT: "God will accomplish his mystery" or "God will complete his secret plan" (See: rc://en/ta/man/translate/figs-activepassive)