“This is evidence of God’s righteous judgment, to make you worthy of the kingdom of God, for which in fact you are suffering.”
2 Thessalonians 1.5
The perseverance and faith of Paul’s readers showed that what God was doing in the world was right. His work prepared them for the eternal kingdom.
We are worthy of the kingdom in the sense that we are being sanctified for it. God makes us ever more holy in order to live in his holy presence.