77 In what follows we have a further recommendation to take this to have been the last manifestation of Himself in bodily fashion which the Lord gave to the apostles. For the same Mark continues in these terms: “And these signs shall follow them that believe: In my name shall they cast out devils; they shall speak with new tongues; they shall take up serpents; and if they drink any deadly thing, it shall not hurt them; they shall lay hands on the sick, and they shall recover.” Then he appends this statement: “So then, after the Lord had spoken unto them, He was received up into heaven, and sat on the right hand of God.
And they went forth, and preached everywhere, the Lord working with them, and confirming the word by signs following.” Now, when he says, “So then, after the Lord had spoken unto them, He was received up into heaven,” he appears probably enough to indicate that this was the last discourse He held with them upon the earth. At the same time, the words do not seem to shut us up to that idea absolutely. For what he says is not, “after He had spoken these things unto them,” but simply, “after He had spoken unto them;” and hence it would be quite admissible, were there any necessity for such a theory, to suppose that this was not the last discourse, and that that was not the last day on which He was present with them upon the earth, but that all the matters regarding which He spoke with them in all these days may be referred to in the sentence, “After He had spoken unto them, He was received up into heaven.”
But, inasmuch as the considerations which we have detailed above lead us rather to conclude that this was the last day, than to suppose that the allusion is specifically to the eleven at a time when, in consequence of the absence of Thomas, they were only ten, we are of opinion that after this discourse which Mark mentions, and with which we have to connect in their proper order those other words, whether of the disciples or of the Lord Himself, which are recorded in the Acts of the Apostles, we must believe the Lord to have been received up into heaven, to wit, on the fortieth day after the day of His resurrection.
Source: The Harmony of the Gospels (New Advent)