The interpretation timeline
Numbers 21:7 Douay-Rheims

Upon which they came to Moses, and said: We have sinned, because we have spoken against the Lord and thee: pray that he may take away these serpents from us. And Moses prayed for the people.

A.D. 45 – 1871 4 witnesses

Patristic

before A.D. 750
45
A.D.
c. 15 B.C.–A.D. 45
“XIX. Why need we enlarge on the pleasures of the belly ? For we may almost say that there are as many varieties of pleasure as there are of gentle flavours which are presented to the belly, and which excite the outward sense. Was it not then, with great propriety that pleasure, which is derived from many varied sources, was presented to an animal endowed with varied faculties ? On this account, too, that part in us which is analogous to the people, and which acts the part of a multitude, when it seeks "the houses in Egypt," that is to say. in its corporeal habitation, becomes entangled in pleasures which bring on death ; not that death which is a separation of soul and body, but that which is the destruction of the soul by vice. For Moses says, " And the Lord God sent among the people deadly serpents, and they bit the people, and a great multitude of the children of Israel died."t For in real truth there is nothing which so much bringeth death upon the soul as an immoderate indulgence in pleasures. And tbat which perishes is not the dominant portion in us but the subject one, that which acts the part of the midtitude ; and it receives death up to this point, namely, until it turns to repentance, and confesses its sin,: for the Israelites, coming to Moses, say. "We have sinned in that we have spoken against the Lord and against you ; pray, therefore, for us to the Lord, and let him take away the serpents from us." It is well put here, not we have sinned because we have spoken against the Lord, but because we were inclined to sin we have spoken against the Numbers xxi. 5. t Numbers xxi. 6. H 2 Lord, for when the mind sins and departs from virtue, it blames divine things, imputing its own sins to God.”
Source

Scholastic

c. 1100 – 1500
1105
A.D.
Rashi Jewish
1040–1105
ויתפלל משה AND MOSES PRAYED — From this we may learn that he of whom one seeks forgiveness should not be so cruel as not to forgive (cf. Midrash Tanchuma, Chukat 19).”

Post-Reformation

c. 1650 – 1900
1771
A.D.
John Gill Reformed
1697–1771
“Therefore the people came to Moses, and said, we have sinned,.... Being bitten with serpents, and some having died, the rest were frightened, and came and made an humble acknowledgment of their sins to Moses: for we have spoken against the Lord, and against thee; murmuring at their being brought out of Egypt, and because they had no better provision in the wilderness; concluding they should die there for want, and never enter into the land of Canaan, of which evils they were now sensible, and confessed them: pray unto the Lord that he take away the serpents from us; or "the serpent" (c), in the singular, which is put for the plural, as it often is; or the plague of the serpent, as the Targum of Jonathan, that it might cease, and they be no more distressed by them: they were sensible they came from God, and that none could remove them but him; and knowing that Moses was powerful in prayer, and had interest with God, they entreat him to be their intercessor, though they had spoken against him and used him ill: and Moses prayed for the people; which proves him to be of a meek and forgiving spirit; who, though he had been so sadly reflected on, yet readily undertakes to pray to God for them. (c) "serpentem", Montanus; "hunc serpentem", Piscator,”
Source
1871
A.D.
1871
“the people came to Moses, and said, We have sinned--The severity of the scourge and the appalling extent of mortality brought them to a sense of sin, and through the intercessions of Moses, which they implored, they were miraculously healed. He was directed to make the figure of a serpent in brass, to be elevated on a pole or standard, that it might be seen at the extremities of the camp and that every bitten Israelite who looked to it might be healed. This peculiar method of cure was designed, in the first instance, to show that it was the efficacy of God's power and grace, not the effect of nature or art, and also that it might be a type of the power of faith in Christ to heal all who look to Him because of their sins (Joh 3:14-15; see also on Kg2 18:4).”
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.