John Gill Commentary Genesis 26:7

"And the men of the place asked him of his wife. And he said, She is my sister. For he feared to say, My wife. Lest, [said he], the men of the place should kill me for Rebekah. Because she was fair to look upon." — Genesis 26:7 (ASV)

And the men of the place asked [him] of his wife The inhabitants of Gerar inquired of Isaac who she was, whether she was his wife or not, or in what relation she stood in to him; this was not a mere civil inquiry, but what arose from the prevalence of lust in them towards her; and yet it was under some restraint, they were not so abandoned to their lusts as to exercise them upon any; not upon a man's wife, the sin of adultery being detestable to them, though that of fornication was made no account of by them:

and he said, she [is] my sister herein imitating his father Abraham in his infirmity and unbelief, who in the same place had made such an answer to a like question concerning Sarah, (Genesis 20:1Genesis 20:2); and if Isaac knew of this, as probably he did, one would wonder that he should fall into the same evil, and especially when he had not so much to say to support his assertion as Abraham had; for Rebekah was not so near akin to him as Sarah was to Abraham; and though cousins might be called sisters, yet this was mere dissimulation to call his wife sister, and was done with an intention to deceive, and therefore not justifiable:

for he feared to say, [she is] my wife which was the real truth; but the fear of men, which brings a snare, led him to this, and good men are not always free from it: lest, [said he], that is, within himself; and so the Targum of Jonathan, he thought in his heart; the men of the place should kill me for Rebekah; that they might marry her, one or other of them; for, it seems, they had not so great a sense of the sin of murder, as of adultery: because she [was] fair to look upon; which he feared would be a temptation to them, and stir up their impure desires after her; he was afraid they would kill him in order to gratify these desires; Rebekah retaining her beauty still, though she had been married in all probability forty years or more, see (Genesis 24:16) .