Mark 16:19

Here is, 1. Christ welcomed into the upper world (Mar 16:19): After the Lord had spoken what he had to say to his disciples, he went up into heaven, in a cloud; which we have a particular account of (Act 1:9), and he had not only an admission, but an abundant entrance, into his kingdom there; he was received up, received in state, with loud acclamations of the heavenly hosts; and he sat on the right hand of God: sitting in a posture of rest, for now he had finished his work, and a posture of rule, for now he took possession of his kingdom; he sat at the right hand of God, which denotes the sovereign dignity he is advanced to, and the universal agency he is entrusted with. Whatever God does concerning us, gives to us, or accepts from us, it is by his Son. Now he is glorified with the glory he had before the world. 2. Christ welcomed in this lower world; his being believed on in the world, and received up into glory, are put together, Ti1 3:16. (1.) We have here the apostles working diligently for him; they went forth, and preached every where far and near.

— Matthew Henry's Concise Commentary (public domain)

So then after the Lord--an epithet applied to Jesus by this Evangelist only in Mar 16:19-20, when He comes to His glorious Ascension and its subsequent fruits. It is most frequent in Luke. had spoken unto them, he was received up into heaven--See on Luk 24:50-51. and sat on the right hand of God--This great truth is here only related as a fact in the Gospel history. In that exalted attitude He appeared to Stephen (Act 7:55-56); and it is thereafter perpetually referred to as His proper condition in glory.

— Jamieson-Fausset-Brown Commentary (public domain)