This is why Saint Paul values every conversion and watches over those converted. This is bound up with his eternal lot and constitutes his appointment in this life. At the same time, he expresses that in his labors and concerns for believers he is not guided by any earthly calculations.
These words are a strong rebuttal to those who, taking advantage of Saint Paul's swift departure, troubled them by saying: he only brought you suffering and abandoned you. The Apostle answers: how could I do this, when my eternal glory lies in their faithfulness to the faith?
Transporting his thought before the face of the Lord at His coming, and presenting Thessalonica with him, the Apostle assures them on the one hand: see to what moment our bond will last. Can one think that it would be broken by such petty circumstances as those that occurred among you? On the other hand, he suggests: my future glory and joy are not mine only, but yours also.
Together we shall rejoice and be glorified. Therefore keep yourselves faithful to the Lord until His coming. For who is a phrase that makes the Apostle's future glory depend conclusively on the faithfulness of the Thessalonians. Yet since he then says, are not you also?, the Apostle does not thereby separate them from the other converts who will serve to crown him with glory at the second coming of Christ.
Chrysostom says: "Are the Macedonians alone your hope, tell me, blessed Paul? They are not alone. Therefore he added: are not you also? So this is not flattery. For he did not simply say, you, but you also, together with others."
Indeed, for him the Philippians too are joy and crown (Phil 4:1), and the Corinthians are his boasting in the day of our Lord Jesus Christ (2 Cor 1:14). Such for him are all the Churches planted and established by him. "Imagine," says Chrysostom, "as far as possible, the whole Church planted and established by Paul. Who would not rejoice over such a multitude and goodness of children?"
Hope, joy, and crown of boasting are different aspects of one and the same moment: standing before the Lord at His second coming. Hope is the support of boldness, by which one dares to stand before Him and not fall prostrate, crying: mountains, fall on us. On what is it established? On conscientious fulfillment, without self-pity, of the works to which one is called, and on the proper use, to God's glory, of the talents entrusted by the Lord to each.
Joy defines the state of the heart when standing before the Lord. For the Apostle there will not be fear, but joy, from the consciousness that his conscience is wholly clean before the Lord. His conscience will assure him that all that depended on him was done without omission or falsity, and it will overshadow his heart with good hope. From this comes the rejoicing of the spirit.
The crown of boasting is the reward that crowns the rejoicing heart with a radiant position in the assembly of glorified saints and angels. The crown of boasting is not that by which one can especially boast, but that for which one will especially be praised. It is a praiseworthy, most praiseworthy crown, a shining glory.
The Lord expresses all three of these aspects in His parable with one saying: "Well done, good and faithful servant. Enter into the joy of your Lord" (Mt 25:21). Theophylact paraphrases Saint Paul's speech thus: "I hope that for your sake I shall be counted worthy of great boldness before Christ the Lord, and of joy, precisely because you both now are and then will be for me a crown of boasting, that is, a crown of shining glory."