John Chrysostom

Then after this he led on to Faith also, that there might not only be hope, but a very true hope. For after the oath he lays down another thing too, even proof by facts, because "the forerunner is for us entered in, even Jesus." But a forerunner is a forerunner of some one, as John was of Christ. Now he did not simply say, "He is entered in," but "where He is entered in a forerunner for us," as though we also ought to attain. …

Homily on Hebrews 11 ↗

Theophylact of Ohrid

Having said that our hope ascends to heaven, he confirms what was said by attesting it with deeds. For He too, Christ, entered; and not simply entered, but entered as a forerunner, that is, as if persuading us that we too must enter. For a forerunner goes ahead of someone following after him, and the distance between the forerunner and those following after him is not great at all, just as between John and Christ. Therefore do not be troubled: soon we too shall enter there, where our forerunner is. …

Commentary on Hebrews ↗

Oecumenius

"where Jesus has entered as a forerunner on our behalf." Having said that our hope enters into heaven, he confirms what has been said, trusting this by the facts. For Christ himself entered there; and not only did he enter, but he entered on our behalf. And where our forerunner has entered, there it is necessary for us also to enter. For the forerunner is the forerunner of those who follow; and the difference between the forerunner and those who follow is not very great, just as between John and Christ. …

The Pseudo-Oecumenian Catena on Hebrews ↗

Thomas Aquinas

325 (cont.). – This, our forerunner, who has entered there, has fixed there; hence, it says in Jn (14:2): 'I go to prepare a place for you.' 'He shall go up that shall open the way before them' (Mic. 2:13). Therefore, he says that Jesus has gone as a forerunner on our behalf within the veil and has fixed our hope there, as it says in the collect of vigil and of Ascension day. …

Commentary on Hebrews ↗