Glossa Ordinaria

Behold, he cometh, etc. And truly you ought to glorify him, because he it is who is to come to reward. With the clouds, that is, with the saints: because they were clouds by raining down doctrine upon others, and by working miracles; or, as he ascended in a cloud, so will he come in a cloud, by which we understand the clemency of God, whereby to the good there is refreshment and illumination, but to the evil terror and blinding. Which also was signified by the cloud by which the children of Israel were led out of Egypt. And they shall see him. Another translation has: All the earth shall see him such. As if he said: They shall see him such as the impious did not believe that he would come. Every eye. The good, that they may rejoice; the evil, that they may be confounded, shall see. They shall bewail. Or they shall be dashed against him, powerless to resist his dominion, after the likeness of a stone and of earthen vessels. Or they shall bewail themselves, that is, they shall grieve looking upon those who are founded upon him, because they shall not grieve so much over the torment itself as that they shall be driven away from such fellowship.