Since he could not do this personally, he entrusted it to his successors, the pastors, just as he entrusted to them the reading of this epistle before all.
We may imagine this moving scene. The pastors of the Thessalonian Church gathered all the Christians together, read the epistle before them, and began to embrace and kiss all of them on behalf of the Apostle.
In other epistles the Apostle asks all to kiss one another (Rom 16:16; 1 Cor 16:20; 2 Cor 13:12; 1 Pet 5:14).
Perhaps this mutual kiss of all took place here also, from joy that the Apostle was alive, remembered them, loved them, and continued to confirm them in communion with the Lord.
So it is on the radiant Resurrection of Christ, as a testimony to the one joy common to all in the resurrection of Christ the Lord.
The Apostle commands them to kiss with a holy kiss. It is such a kiss as saints may give to saints, and as it is fitting for saints to receive from saints.
It is given in purity of heart, with reverence toward one another as persons who bear God within themselves.
Or by "holy kiss" he means the kiss of love, as Saint Peter does (1 Pet 5:14), in contrast to the kiss of betrayal, such as that of Judas (Oecumenius).
Saint Chrysostom sees in this word of the Apostle an impulse for all of us to preserve mutual love. This love makes even those separated by distance inseparable.
"Preserve in yourselves the fire of love. Distance is no obstacle to it. Rather, love fills with itself all the space that separates it from the beloved object, and is present everywhere."