The Liturgy for the Last Sunday of Pentecost features the following warning: "He Who came in Mercy shall return in Justice."
"Amen, I say to you, that this generation shall not pass till all these things be done: heaven and earth shall pass, but My words shall not pass, saith the Lord.”
Our Lord came in humility, but He will return in glory; the object of His first coming being to prepare for the second. Those who receive Him gladly in time will be welcomed by him when eternity begins; while those who refused to acknowledge Him will be rejected.
For this reason the prophets do not make any clear distinction between the two comings of the Messias, since they are but two acts of the same divine drama. In the same way our Lord does not separate the destruction of Jerusalem from the end of the world, since the chastisement which fell upon the Jews in a symbol of the eternal punishment which will reach all those who have rejected our divine Redeemer. The first coming has taken place, the second is yet to come. Let us prepare for it. That is the tenor of today’s Gospel.
With this account of the Last Judgment, closes the Temporal Cycle of the liturgical year which began on the first Sunday of Advent and ends today. Ever since Advent, the Church has been concerned with the preparation for these two comings of mercy and justice, for she never separates them. Never is this subject absent from her thoughts, least of all on this last Sunday; for if Christ came once at His first coming to save us, it was that we might enter heaven in His glorious train when he comes once more at the end of time. This will be the true Pasch, the full passing into the real land of promise, of which this concluding Sunday is the figure and the type.
Source: Dom Gaspar Lefebvre, OSB, 1945, adapted and abridged.