Paul uses what I find to be a hard phrase as he speaks of trials: "That you may be counted worthy..." My heart is pierced as I read it for I know that my response to trials often reveals unworthiness. Praise God for grace and growth! What I look at as failure, God looks at as learning. The more deeply I understand that trials have purpose and potential, the greater my faith and love will be!
Paul went onto say that the believers' hope-filled endurance of trials (which are tokens of God's judgment), gave opportunity for others to see the glory of God. That's a powerful encouragement when trials come--they have a glorious purpose! The Father desires that none shall perish; when He entrusts a trial to us, it is so another soul might be brought into the Kingdom. Rejoicing in the growing faith of others is right--for it is simply rejoicing in the increasing visibility of the King!