Each rung of the ladder of being involves overcoming of the ontological division between the abstract and the concrete.
1.) Natural things. On the lowest level of being, both the abstract and the concrete cannot both be real. Among sensible things, we either have to say, with Aristotle, that the concrete is real and the abstract is a mere logical being that has existence only secondarily to the concrete; or we say with Plato that the intelligible world is real and concrete sensible things are secondary and purely participatory existences.
2.) The human intellect. The human intellect is the first realm in which the ontological opposition between abstract and concrete begins to break down. Is my abstract idea abstract or concrete (i.e. “mine”)? When I know DNA, do I know it by the idea in my head or by the same idea as you? The questions are all false dichotomies because the human mind transcends the ontological oppositions we find in natural things. Nevertheless, our mind is still the form of a natural body, and as such it mires us in the oppositions we find in #1.
3.) The angelic intellect. Angels overcome the concretion of substance that we find in each human person. In the angel, the reality of the substance is no longer opposed to the reality of the species, but both express their proper perfection in one and the same angel. Nevertheless, the angel is one and only one concrete substance, and so is divided from the substance of others, even if not from his own intelligible, abstract character.
4.) The triune God. The definitive overcoming of the opposition between the concrete and the abstract occurs not only in the doctrine of divine simplicity (where we understand God’s existence through concrete terms and his simplicity by abstract ones) but also in the fact that the existence of one individual is no longer disconnected from the existence of another, i.e. abstraction comes to full flower by preserving its absolute unity while communicating itself to more than one substance, as opposed to angelic nature, which is too restricted to be fully communicated to more than one.