This is an obvious sign of the righteous judgment of God, to the end that you may be counted worthy of the Kingdom of God, for which you also suffer.
It is very important to watch out for modern versions, translations, and paraphrases at this point of the verse because the Calvinistic teaching of rapture, tribulation, millennium etc. becomes evident. An effort is made to show the "kingdom" is in the future and not in existence now.