In 1 Thessalonians 3:11-13, Paul is praying for his return to Thessalonica and for Jesus to increase the Thessalonians' love for each other and for all people. By doing so, the result of the increased love will strengthen their hearts to be blameless in holiness in the presence of God when Jesus comes.
The end of 1 Thessalonians 3:11 states:
...ἐν τῇ παρουσίᾳ τοῦ κυρίου ἡμῶν Ἰησοῦ μετὰ πάντων τῶν ἁγίων αὐτοῦ.
...in the coming of our Lord Jesus with all of his holy ones.
This phrase is an allusion to o the end of Zechariah 14:5 LXX:
...καὶ ἥξει κύριος ὁ θεός μου καὶ πάντες οἱ ἅγιοι μετ᾿ αὐτοῦ.
...and the Lord (Yahweh) my God will come and all the holy ones with him.
In Zechariah 14, it is Yahweh who will come set foot of the mount of Olives, but in 1 Thessalonians 3:11, Paul replaces Yahweh with Jesus in his allusion to Zechariah 14:5.
Perhaps a better translation would be to include what is inferred by Paul's use of ὁ κύριος (The Lord):
...in the coming of our Yahweh Jesus with all of his holy ones.