Notes on the Bible, by Albert Barnes, [1834], at sacred-texts.com
The "fathers" are, as in Deu 4:37, the patriarchs, Abraham, Isaac, and Jacob. With them God did indeed make a covenant, but not the particular covenant now in question. The responsibilites of this later covenant, made at Sinai by the nation as a nation, attached in their day and generation to those whom Moses was addressing.
Compare Exo. 20 and notes.
Moses here adopts the Ten Words as a ground from which he may proceed to reprove, warn, and exhort; and repeats them, with a certain measure of freedom and adaptation. Our Lord Mar 10:19 and Paul Eph 6:2-3 deal similarly with the same subject. Speaker and hearers recognized, however, a statutory and authoritative form of the laws in question, which, because it was familiar to both parties, needed not to be reproduced with verbal fidelity.
The exhortation to observe the Sabbath and allow time of rest to servants (compare Exo 23:12) is pointed by reminding the people that they too were formerly servants themselves. The bondage in Egypt and the deliverance from it are not assigned as grounds for the institution of the Sabbath, which is of far older date (see Gen 2:3), but rather as suggesting motives for the religious observance of that institution. The Exodus was an entrance into rest from the toils of the house of bondage, and is thought actually to have occurred on the Sabbath day or "rest" day.
The blessing of general well-being here annexed to the keeping of the fifth commandment, is no real addition to the promise, but only an amplification of its expression.
The "field" is added to the list of objects specifically forbidden in the parallel passage Exo 20:17. The addition seems very natural in one who was speaking with the partition of Canaan among his hearers directly in view.
He added no more - i. e., He spoke no more with the great voice directly to the people, but addressed all other communications to them through Moses. This unique and sublime phenomenon, followed up by the inscription of the Ten Words on the two tables by the finger of God, marks not only the holiness of God's Law in general, but the special eminence and permanent obligation of the Ten Words themselves as compared with the rest of the Mosaic enactments. The giving of the two tables did not take place until Moses had been on the Mount 40 days and 40 nights, as appears from the fuller account of Deu 9:9-12.
These verses contain a much fuller narrative of the events briefly described in Exo 20:18-21. Here it is important to call attention to the fact that it was on the entreaties of the people that Moses had taken on him to be the channel of communication between God and them. God approved Deu 5:28 the request of the people, because it showed a feeling of their own unworthiness to enter into direct communion with God. The terrors of Sinai had done their work; they had awakened the consciousness of sin.