The interpretation timeline
Luke 21:28 Douay-Rheims

But when these things begin to come to pass, look up, and lift up your heads, because your redemption is at hand.

A.D. 339 – 1871 7 witnesses 11 excerpts

Patristic

before A.D. 750
339
A.D.
c. A.D. 260–339
“Or else, To those that have passed through the body and bodily things, shall be present spiritual and heavenly bodies: that is, they will have no more to pass the kingdom of the world, and then to those that are worthy shall be given the promises of salvation. For having received the promises of God which we look for, we who before were crooked shall be made upright, and we shall lift up our heads who were before bent low; because the redemption which we hoped for is at hand; that namely for which the whole creation waiteth.”
Source
“He speaks these things to His disciples, not as to those who would continue in this life to the end of the world, but as if uniting in one body of believers in Christ both themselves and us and our posterity, even to the end of the world.”
“For as in this life, when winter dies away, and spring succeeds, the sun sending forth its warm rays cherishes and quickens the seeds hid in the ground, just laying aside their first form, and the young plants sprout forth, having put on different shades of green; so also the glorious coming of the Only-begotten of God, illuminating the new world with His quickening rays, shall bring forth into light from more excellent bodies than before the seeds that have long been hidden in the whole world, i. e. those who sleep in the dust of the earth. And having vanquished death, He shall reign from henceforth the life of the new world.”
Source
“Or by generation He means the new generation of His holy Church, shewing that the generation of the faithful would last up to that time, when it would see all things, and embrace with its eyes the fulfilment of our Saviour’s words.”
397
A.D.
Ambrose of Milan Patristic
A.D. 339–397
“Matthew speaks of the fig-tree only, Luke of all the trees. But the fig-tree shadows forth two things, either the ripening of what is hard, or the luxuriance of sin; that is, either that, when the fruit bursts forth in all trees and the fruitful fig-tree abounds, (that is, when every tongue confesses God, even the Jewish people confessing Him,) we ought to hope for our Lord’s coming, in which shall be gathered in as at summer the fruits of the resurrection. Or, when the man of sin shall clothe himself in his light and fickle boasting as it were the leaves of the synagogue, we must then suppose the judgment to be drawing near. For the Lord hastens to reward faith, and to bring an end of sinning.”
Source
604
A.D.
Gregory the Great Patristic
c. A.D. 540–604
“(Hom. 1. in Ev.) Having in what has gone before spoken against the reprobate, He now turns His words to the consolation of the elect; for it is added, When these things begin to be, look up, and lift up your heads, for your redemption draweth nigh; as if he says, When the buffettings of the world multiply, lift up your heads, that is, rejoice your hearts, for when the world closes whose friends ye are not, the redemption is near which ye seek. For in holy Scripture the head is often put for the mind, for as the members are ruled by the head, so are the thoughts regulated by the mind. To lift up our heads then, is to raise up our minds to the joys of the heavenly country.”
Source
“(in Hom. 1. in Ev.) But all the things before mentioned are confirmed with great certainty, when He adds, Verily I say unto you, &c.”
735
A.D.
Bede the Venerable Patristic
c. A.D. 672–735
“He strongly commends that which he thus foretels. And, if one may so speak, his oath is this, Amen, I say unto you. Amen is by interpretation “true.” Therefore the truth says, I tell you the truth, and though He spoke not thus, He could by no means lie. But by generation he means either the whole human race, or especially the Jews.”
Source

Scholastic

c. 1100 – 1500
1107
A.D.
c. 1055–1107
“That is, perfect liberty of body and soul. For as the first coming of our Lord was for the restoration of our souls, so will the second be manifested unto the restoration of our bodies.”

Post-Reformation

c. 1650 – 1900
1771
A.D.
John Gill Reformed
1697–1771
“For as a snare shall it come,.... In which a bird is suddenly taken, and cannot get out again; the Persic version renders it, "as lightning and the splendour of the sun"; which break out at once, and enlighten the whole earth; so the destruction of the Jewish nation should be sudden and unavoidable, and universal; for it should come on all them that dwell upon the face of the whole earth: or land of Judea; and so it was, for not only Jerusalem, but all Judea, and Galilee, suffered in this desolation.”
Source
1871
A.D.
1871
“redemption--from the oppression of ecclesiastical despotism and legal bondage by the total subversion of the Jewish state and the firm establishment of the evangelical kingdom (Luk 21:31). But the words are of far wider and more precious import. Matthew (Mat 24:30) says, "And then shall appear the sign of the Son of man in heaven," evidently something distinct from Himself, mentioned immediately after. What this was intended to mean, interpreters are not agreed. But as before Christ came to destroy Jerusalem, some appalling portents were seen in the air, so before His personal appearing it is likely that something analogous will be witnessed, though of what nature it is vain to conjecture.”
Source
Modern · 1953 →

The in-app commentary runs from the Fathers to the early-modern record, then stops — that's where the public-domain sources end, not where the reading does. For the modern reading, follow the sources directly.