"Without doubt the angel sinned by seeking to be as God. But this can be understood in two ways: first, by equality; secondly, by likeness. He could not seek to be as God in the first way, because by natural knowledge he knew that this was impossible, and there was no habit preceding his first sinful act, nor any passion fettering his knowing power, so as to lead him to choose what was impossible. . . . And even supposing it were possible, it would be against the natural desire, because there exists in everything the natural desire of preserving its own being, which would not be preserved were it to be changed into another nature. . . . But he desired to be like God in this respect,--by desiring, as his last end of happiness [(ut finem ultimum beatitudinis)] that which he could attain by the power of his own nature [(virtute suae naturae)], turning his desire away from supernatural happiness [(a beatitudine supernaturali)], which is attained by God's grace [(ex gratia Dei)]. Or, if desiring as his last end that likeness to God which is bestowed by grace, he sought to have it by the power of his own nature, and not from divine assistance according to God's ordering [(per virtutem suae naturae, non ex divino auxilio secundum Dei dispositionem)]."
Thomas Aquinas, Summa theologiae I.63.3.Resp., trans. FEDP. A rejection of what I take to be the popular claim, that Lucifer sought to be like God simpliciter. (Although Aquinas is really responding in the nuanced positive to the objections here, the question being "Whether the Devil desired to be as God".) I was put onto this by Ph. Vallin, "Henri de Lubac et Saint Thomas d'Aquin: ouverture et structure en théologie," Revue des sciences religieuses 77, no. 2 (2003): 221-222, who goes on to stress a point I am myself (perhaps overly) fond of making, that "the obstacle . . . of the transcendent heteronomy of salvation" is "an illusion, . . . as if the Being of God were a member of [and therefore a threat to the autonomy of the other members of (faisait nombre avec) the class] of autonomous being[s]" (222, where Suarez and Wolf, not Aquinas, are the culprits). "Saint Thomas finds already in Aristotle a correction of the principle that the idea of nature implies that of complete autonomy and loaths heteronomy". No, human nature is a "structure open" to the "opening structure" of divine revelation (225, 226). "the anthropology of the open structure" discovers its (undeniably cruciform) fulfillment in the "revelation of the trinitarian economy to which it is subordinated: 'before Abraham was, I AM'" (226: Abraham, "open structure"; YHWH, "opening structure"). For more on the sign of contradiction that this "opening structure" presents, go here: http://liberlocorumcommunium.blogspot.com/2008/12/corrective-on-aquinas-worth-heeding.html.