This sacrament is presented under two species for three reasons: first, indeed, on account of its perfection, because, since it is spiritual refreshment, it ought to be spiritual food and spiritual drink. For even bodily refreshment is not complete without food and drink. Hence he also says above: and did all eat the same spiritual food: and all drank the same spiritual drink (1 Cor 10:3-4).
Second, on account of its signification. For it is the memorial of the Lord's passion, through which the blood of Christ was separated from his body; that is why in this sacrament the blood is offered separately from the body.
Third, on account of the salutary effect of this sacrament, for it avails for the health of the body, and so the body is offered; and it avails for the health of the soul, and so the blood is offered. For the soul is in the blood (Lev 17:11).
[St. Thomas Aquinas, Commentary on the Letters of Saint Paul to the Corinthians, Larcher, Mortensen, and Keating, trs., The Aquinas Institution for the Study of Sacred Doctrine (Lander, WY: 2012) p. 244. This is from the commentary on I Corinthians.]
And today is the end of Lent.
