Комментарий к Берешит 21:24

אנכי אשבע, I will do you the favour to swear such an oath; however, you have not done me any favours as you claim to have done.

ויאמר אברהם אנכי אשבע. Abraham said: "I will swear." Abraham implied that he could counter Avimelech's arguments but had decided instead to swear as Avimelech requested.

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.

Swear to me here by Elokim. Avimelech was confident that once Avraham swore, Hashem would never command him to violate his oath.

אנכי אשבע, “I am ready to swear to this.” Avraham does not acknowledge that Avimelech had done him any favours, seeing that his servants had repeatedly stolen the wells he had dug and he had done nothing about it (Compare verse 25).

In consideration of Abraham's intention to rebuke Avimelech (verse 25), he thought that if he did this immediately Avimelech would interpret Abraham's attitude as a denial of the favours the king claimed to have done for him. He decided therefore to state first of all that he was willing to swear the oath in question.

Another way of looking at the verse is that Abraham accepted the oath only for himself, i.e. אנכי; he was not prepared to commit his son or grandson as had been requested by Avimelech.