What does 1 Thessalonians 3:13 mean?

We also pray that God will make your hearts strong and blameless in holiness, so you'll be ready to stand before our God and Father when our Lord Jesus comes back with all those who belong to Him. 1 Thessalonians 3:13 - Modern Text Bible

(Paul's ultimate hope is that they'll be spiritually mature and pure, ready for Jesus' return along with all believers.)