19 . . . and behold I am with you all days, even to the consummation of the world.
Chrysostom: Because what He had laid upon them was great, therefore to exalt their spirits He adds, “And, lo, I am with you always, even unto the end of the world.” As much as to say, Tell Me not of the difficulty of these things, seeing I am with you, Who can make all things easy. A like promise He often made to the Prophets in the Old Testament, to Jeremiah who pleaded his youth, to Moses, and to Ezekiel, when they would have shunned the office imposed upon them. And not with them only does He say that He will be, but with all who shall believe after them. For the Apostles were not to continue till the end of the world, but He says this to the faithful as to one body.
He brings before them the end of the world, that He may the more draw them on, and that they may not look merely to present inconveniences, but to the infinite goods to come. As much as to say, The grievous things which you shall undergo, terminate with this present life, seeing that even this world shall come to an end, but the good things which ye shall enjoy endure for ever.
Rabanus: Hence we understand that to the end of the world shall not be wanting those who shall be worthy of the Divine indwelling.
Bede: He who remains in this present world with His elect, protecting them, the same will continue with them after the end, rewarding them.
Jerome: He then who promises that He will be with His disciples to the end of the world, shews both that they shall live for ever, and that He will never depart from those that believe.
Leo: By ascending into heaven He does not desert His adopted; but from above strengthens to endurance, those whom He invites upwards to glory.
Scripture from the Douay-Rheims Bible. Commentary from St. Thomas Aquinas, Catena Aurea, Vol. I (London: Rivington, 1842).