"We ought always to give thanks to God for you, brothers, as is right, because your faith is growing abundantly, and the love of every one of you for one another is increasing.
Therefore we ourselves boast about you in the churches of God for your steadfastness and faith in all your persecutions and in the afflictions that you are enduring.
This is evidence of the righteous judgment of God, that you may be considered worthy of the kingdom of God, for which you are also suffering--"
The Thessalonians didn't "have to do" anything to make themselves 'worthy.' They were already worthy because God Himself loved them and accounted them 'worthy.'
"To this end we always pray for you, that our God may make you worthy of his calling and may fulfill every resolve for good and every work of faith by his power, so that the name of our Lord Jesus may be glorified in you, and you in him, according to the grace of our God and the Lord Jesus Christ."
That is the essence of grace. God accounts us "worthy" when we were truly worthless. He then goes on to transform us by His grace to make us into a vessel "worthy of honor" (Romans 9:21-23).
Am I worthless?
__________________
Hebrews 13:23 Know ye that our brother Timothy is set at liberty