And, indeed, she desired him, and he desired her; [and he would have succumbed] had he not seen [in this temptation] an evidence of his Sustainer's truth:23
thus [We willed it to be] in order that We might avert from him all evil and all deeds of abomination - for, behold, he was truly one of Our servants.24
The interpolated phrase "and he would have succumbed", is, according to Zamakhshari, implied in the above sentence. In his commentary on this verse, he further points out that the moral significance of "virtue" consists in one's inner victory over a wrongful desire, and not in the absence of such a desire. Cf. the well-known saying of the Prophet, recorded, on the authority of Abu Hurayrah, by Bukhari and Muslim: "God, exalted be He, says: 'If a servant of Mine [merely] desires to do a good deed, I shall count this [desire] as a good deed; and if he does it, I shall count it tenfold. And if he desires to commit a bad deed, but does not commit it, I shall count this as a good deed, seeing that he refrained from it only for My sake...'" - i.e., in consequence of a moral consideration (which, in the present instance, is described as "an evidence of God's truth").
Lit., "he was among Our sincere servants".