Genesis 21:24

Gen 21:24 And Abraham said, I will swear.

Ver. 24. I will swear.] Abraham quickly consents to so reasonable a request, from so honourable a person. The wisdom from above is "easy to be entreated". {Jas 3:17} The churl Nabal holds it a goodly thing to hold off. It is but manners to reciprocate: very publicans can find in their hearts to do good to those that have been good to them. {Mat 5:46-47}

John Trapp, A Commentary or Exposition upon All the Books of the Old and New Testament (1647–1656) — public domain. Text from a community e-Sword module.

So that it is a lawful thing to take an oath in matters of importance, for to justify the truth, and to assure others of our sincerity.

Geneva Bible (1599) marginal notes — public domain. Text via Bolls.life.

24. And Abraham said, I will swear. Although he had the stronger claim of right, he yet refuses nothing which belonged to the duty of a good and moderate man. And truly, since it is becoming in the sons of God to be freely ready for every duty; nothing is more absurd, than for them to appear reluctant and morose, when what is just is required of them. He did not refuse to swear, because he knew it to be lawful, that covenants should be ratified between men, in the sacred name of God. In short, we see Abraham willingly submitting himself to the laws of his vocation.

John Calvin's Commentaries (1540-1563) — public domain. Text from the Calvin Translation Society English edition (1840s-50s) via the Christian Classics Ethereal Library (ccel.org). Calvin's coverage is partial (roughly two-thirds of the Bible); uncommented books and verses are honest gaps, never fabricated. The 19th-century editor's footnotes and remarks are omitted so the notes are faithfully Calvin's own voice.

And Abimelech said, I wot not who hath done this thing,.... He pleads ignorance; he knew nothing of it before, nor now which of his servants had done it; intimating, that if he could know who it was, he should severely reprimand him for it:

neither didst thou tell me: signifying that he was to blame he did not complain of it sooner; and at least he had no reason to blame him, since he had never informed him before of it, and therefore could not expect to be redressed:

neither yet heard of it but today: he had not heard of it from others, as the Targum of Jonathan rightly adds, by way of explanation, but that very day, and very probably not till the moment he had it from Abraham himself.

John Gill's Exposition of the Whole Bible (1746–1763) — public domain (CC PDM 1.0). Text via the HelloAO Bible API.

I will swear. The matter was of sufficient importance. Abraham binds himself, but not his posterity, who by God’s order fought against the descendants of this king.

George Leo Haydock (1774–1849), Haydock's Catholic Family Bible and Commentary, 1859 edition — public domain. Excludes Psalms (Douay-Rheims chapter numbering differs from Protestant) and Deuterocanonical books (Catholic canon only).

Quest. How could Abraham lawfully swear this, when Canaan was given by God to him and his seed for ever?

Answ. Neither Abraham nor his seed had any present and actual right to the possession of the land, but only the promise of a right in it, and possession of it after some hundreds of years, and therefore he gave away none of his right by this oath. For this oath did only oblige Abraham, and not his posterity; and Abimelech extended that obligation no further than to his son’s son.

Matthew Poole's English Annotations on the Holy Bible (1683–1685) — public domain. Text from a community e-Sword/MySword module.

And Abraham said, I will swear. Only before concluding the agreement there was a matter of a more personal character that required settlement.

The Pulpit Commentary (1880–1919), ed. H.D.M. Spence-Jones & Joseph S. Exell — public domain. Text from a community e-Sword module.

ויאמר אברהם אנכי אשבע, implying that Avimelech on his part has to swear also. The word אשבע is spelled with the vowel chirik under the letter א, Generally, when a verb in the first person is in the passive mode, it has the vowel segol so that the combination of aleph-chirik should not be misunderstood as if it had been spelled אי.

Radak on the Tanakh — English translations: “Sefaria Community Translation” (CC0 1.0 (public-domain dedication)); “Eliyahu Munk, HaChut Hameshulash” (CC BY 4.0); “Rabbi Mike Feuer, Jerusalem Anthology” (CC BY 4.0); and “R. David Kimhi on the first book of Psalms, Translated by R.G. Finch, London, 1919” (public domain). Text via Sefaria.