The originatively original world (the one ex nihilo) must not be confused with this one, the Redemptive world and its creation (notably dealt with in Genesis). In the perfect finite world that God originatively created, each person [angelic or human…and the distinction between angels and humans ontologically was somewhat discerned by Aquinas] had to be perfect in being and in freedom. Perfect freedom is not the same as perfect goodness, perfect power, or even perfect beauty. It is a distinctive attribute, whether said of God (infinitely perfect freedom) or of creatures (finitely perfect freedom. The exercise of our perfect freedom at the moment of creation ex nihilo, then, was ours to do. God does God’s infinitely perfect free acts; we must do our finitely perfect free act–at that juncture we were finitely perfectly free as gifted by God.But as received by us–in our very first act of being and doing: our receiving of our own unique gifted being–we imperfected ourselves and became the ultimate, uncaused cause of all our pain, misery, and suffering. (Not the only cause, but the ultimate cause.) Our act was imperfect. We acted imperfectly with our perfect, God-gifted freedom. The perfect freedom-power did not act; nor did the act act. WE did. WE imperfected ourselves by responding to the gift of being by ‘saying’ less than fully yes. Thank God…er, rather thank ourselves…for not saying fully no! [It was all our finite perfect freedom; not at all God’s. God gives us OUR OWN BEING AND FREEDOM, not a particle of His–we are not mini-pantheists, I hope.
So we can say that we originatively, ex nihilo, in receiving our being [[by the way, creation ex nihilo is a necessarily interpersonal act on God’s part, necessarily intending the person being created as a person and requiring a fully responsible personal response from that person…Can you conceive of an act of more potential intimacy than that of gifting another (albeit finite) person with his or her be-ing at all and be-ing this unique one?!]]
…in receiving our being, we damaged our functional freedom–not our natural freedom, God gifted such forever–such that we crashed our whole being and were ontologically comatose until God’s Redemptive Creation called for our conception in a particular space and time on the way to recovery via redemption by Christ and potential salvation.
Even our “creation out of nothing” notions seem to treat God as a grand “Aritisan” of the world without any necessarily personal response on the part of the ones being created!! How impersonal can we get regarding origins!!
As for our motivation for saying maybe (less than fully yes) to the gift of our perfect being, we were perfectly free to know and will our being as gifted by God or to will to be
an infinitely perfect being, like God, with whom we were face to face in truth (though not in glory…God’s glory would come immediately if we had said fully yes; as it is we will have to wait for knowing and loving God in His glory if and when we repent fully through the purgatory of this world and probably of the Purgatory in the next world. Hey, perhaps we could say that, being in the presence of the Triune God at that supremely intimate moment of creation ex nihilo, we let ourselves tempt ourselves to want to be a fourth person of the Blessed Trinity! And some actually willed such (“I want to be one of You, God!”)

The question that fhansen raises about how we could be perfectly free and yet choose less than perfectly is an ancient one raised by Maximus the Confessor et al. But I would reply: how could we be PERFECTLY free, yet finite, were we not able to “choose” less than perfectly AT THAT POINT. Once our perfect “choice” or willing act is effected, then we are that way forever, confirmed in beatitude.
Will stop here, but have much more to say, if anyone wishes to ‘hear’ and discuss.