The interpretation timeline
Deuteronomy 26:18 Douay-Rheims

And the Lord hath chosen thee this day, to be his peculiar people, as he hath spoken to thee, and to keep all his commandments:

A.D. 215 – 1771 4 witnesses

Patristic

before A.D. 750
215
A.D.
c. A.D. 150–215
“These are evidently symbolic—hands, of action; heart, of deliberation; mouth, of speech. There is an excellent text on the subject of the penitent: "You have chosen God today to be your God, and the Lord has chosen you today to be his people." God makes his own the person who is eager to serve truth and reality and comes as a suppliant. Even if he is only one in number, he is honored on equal terms with the whole people. He is a part of the people. He becomes the complement of the people once he is reestablished out of his previous position, and the whole in fact takes its name from the part.”
Source

Scholastic

c. 1100 – 1500
1105
A.D.
Rashi Jewish
1040–1105
כאשר דבר לך AS HE HATH PROMISED THEE — in the words (Exodus 19:5) “Ye shall be a select portion unto Me” (Mekhilta).”
1270
A.D.
Ramban Jewish
1194–1270
“AND THE ETERNAL HATH AVOUCHED THEE. For this day is to you as the day of [the Revelation on] Sinai, and G-d exalted and magnified you by your acceptance of the Torah in order that you be His own treasure from among all peoples, and that thou shouldest keep all His commandments, for, to you alone He gave His Torah and commanded you with all the commandments that are desireable before Him and to no other nation. It is similar to what is written, He declareth His word unto Jacob, His statutes and His ordinances unto Israel. He hath not dealt so with any nation.”
Source

Post-Reformation

c. 1650 – 1900
1771
A.D.
John Gill Reformed
1697–1771
“And the Lord hath avouched thee this day to be his peculiar people,.... Affirmed and declared them to be his special people, above all people on the face of the earth, and that they were looked upon and considered by him as his jewels, his peculiar treasure: as he hath promised thee; on condition of their obedience to him, as he did in Exo 19:5, and that thou shouldest keep all his commandments; at the same time declared this as his will, that they should observe all his precepts, to which they were laid under obligation by the special favour and peculiar privileges he bestowed upon them, Deu 7:6. The Targums interpret both these verses of the people of Israel choosing and making the Lord their King, and of his being made King over them; and so it respects their peculiar form of civil government, being a theocracy. The Lord's people in Christ are a peculiar people; they are distinct from all people, and are peculiarly regarded by him; they are the objects of his peculiar love, and receive peculiar favours from him; and whom having chosen and redeemed, he calls by his special grace, and witnesses their special relation to him by his Spirit; which grace obliges and excites them to a cheerful obedience to his commands.”
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.