| Barnes' Notes on the Bible Abimelek observes Isaac sporting with Rebekah as only husband and wife should, constrains him to confess that she is his wife, charges him with the impropriety of his conduct, and commands his people to refrain from harming either of them on pain of death. We see how insecure a female's honor was in those days, if she was in a strange land, and had not a band of men to keep back the hand of violence. We perceive also that God mercifully protects his chosen ones from the perils which they bring upon themselves by the vain self-reliance and wicked policy of the old corrupt nature. This remnant of the old man we find in the believers of old, as in those of the present time, though it be different and far less excusable in its recent manifestations.
Clarke's Commentary on the BibleIsaac was sporting with Rebekah his wife - Whatever may be the precise meaning of the word, it evidently implies that there were liberties taken and freedom used on the occasion, which were not lawful but between man and wife.
Gill's Exposition of the Entire BibleAnd it came to pass, when he had been there a long time,.... Perhaps some years: for though it is in the original, "when days were prolonged to him there" (b); yet days are sometimes put for years: that Abimelech king of the Philistines looked out at a window; in his own palace, near to which, in all likelihood, were the apartments that Isaac and Rebekah dwelt in; and this he did accidentally, and not out of curiosity, or with any intention to observe or pry into the behaviour and conduct of these two persons one towards the other: and saw, and, behold, Isaac was sporting with Rebekah his wife; laughing and joking with her, which by his motions and gestures, and the airs and freedoms he took, Abimelech could perceive were such as were not usual between brothers and sisters, though honest and lawful between man and wife; such as embracing her in his arms, and frequently kissing her, and the like. (b) "cum prolongati essent ei ibi dies", Pagninus, Montanus, Schmidt.
Geneva Study BibleAnd it came to pass, when he had been there a long time, that Abimelech king of the Philistines looked out at a window, and saw, and, behold, Isaac was {e} sporting with Rebekah his wife. (e) Or showing some familiar sign of love, by which it might be known that she was his wife.
Wesley's Notes 26:8 This Abimelech was not the same that was in Abraham's days, Ge 20:2 - 18, for this was near an hundred years after, but that was the common name of the Philistine kings, as Caesar of the Roman emperors.
Matthew Henry's Concise Commentary26:6-11 There is nothing in Isaac's denial of his wife to be imitated, nor even excused. The temptation of Isaac is the same as that which overcame his father, and that in two instances. This rendered his conduct the greater sin. The falls of those who are gone before us are so many rocks on which others have split; and the recording of them is like placing buoys to save future mariners. This Abimelech was not the same that lived in Abraham's days, but both acted rightly. The sins of professors shame them before those that are not themselves religious.
Matthew Henry's Whole Bible CommentaryVerses 6-11 Isaac had now laid aside all thoughts of going to Egypt, and, in obedience to the heavenly vision, sets up his staff in Gerar, the country in which he was born (v. 6), yet there he enters into temptation, the same temptation that his good father had been once and again surprised and overcome by, namely, to deny his wife, and to give out that she was his sister. Observe, I. How he sinned, v. 7. Because his wife was handsome, he fancied the Philistines would find some way or other to take him off, that some of them might marry her; and therefore she must pass for his sister. It is an unaccountable thing that both these great and good men should be guilty of so strange a piece of dissimulation, by which they so much exposed both their own and their wives' reputation. But we see, 1. That very good men have sometimes been guilty of very great faults and follies. Let those therefore that stand take heed lest they fall, and those that have fallen not despair of being helped up again. 2. That there is an aptness in us to imitate even the weaknesses and infirmities of those we have a value for. We have need therefore to keep our foot, lest, while we aim to tread in the steps of good men, we sometimes tread in their by-steps. II. How he was detected, and the cheat discovered, by the king himself. Abimelech (not the same that was in Abraham's days, ch. 20, for this was nearly 100 years after that, but this was the common name of the Philistine kings, as Caesar of the Roman emperors) saw Isaac more familiar and pleasant with Rebekah than he knew he would be with his sister (v. 8): he saw him sporting with her, or laughing; it is the same word with that from which Isaac has his name. He was rejoicing with the wife of his youth, Prov. 5:18. It becomes those in that relation to be pleasant with one another, as those that are pleased with one another. Nowhere may a man more allow himself to be innocently merry than with his own wife and children. Abimelech charged him with the fraud (v. 9), showed him how frivolous his excuse was and what might have been the bad consequences of it (v. 10), and then, to convince him how groundless and unjust his jealousy of them was, took him and his family under his particular protection, forbidding any injury to be done to him or his wife upon pain of death, v. 11. Note, 1. A lying tongue is but for a moment. Truth is the daughter of time; and, in time, it will out. 2. One sin is often the inlet to many, and therefore the beginnings of sin ought to be avoided. 3. The sins of professors shame them before those that are without. 4. God can make those that are incensed against his people, though there may be some colour of cause for it, to know that it is at their peril if they do them any hurt. See Ps. 105:14, 15. | 
