The glory of God is man fully alive.
Too all-encompassing a notion to grasp. But I instinctively knew what the opposite of a "man fully alive" was:
a spiritual sickness perfectly explained by Catholic Encyclopedia (emphasis mine):
One of the seven capital sins. In general it means disinclination to labour or exertion. As a capital or deadly vice St. Thomas (II-II:35) calls it sadness in the face of some spiritual good which one has to achieve (Tristitia de bono spirituali). Father Rickaby aptly translates its Latin equivalent acedia (Gr. akedia) by saying that it means the don't-care feeling. A man apprehends the practice of virtue to be beset with difficulties and chafes under the restraints imposed by the service of God. The narrow way stretches wearily before him and his soul grows sluggish and torpid at the thought of the painful life journey. The idea of right living inspires not joy but disgust, because of its laboriousness. This is the notion commonly obtaining, and in this sense sloth is not a specific vice according to the teaching of St. Thomas, but rather a circumstance of all vices. Ordinarily it will not have the malice of mortal sinfulness, of course, we conceive it to be so utter that because of it one is willing to bid defiance to some serious obligation. St. Thomas completes his definition of sloth by saying that it is torpor in the presence of spiritual good which is Divine good. In other words, a man is then formally distressed at the prospect of what he must do for God to bring about or keep intact his friendship with God. In this sense sloth is directly opposed to charity. It is then a mortal sin unless the act be lacking in entire advertence or full consent of the will. The trouble attached to maintenance of the inhabiting of God by charity arouses tedium in such a person. He violates, therefore, expressly the first and the greatest of the commandments: "Thou shalt love the Lord thy God with thy whole heart, and with thy whole soul, and with thy whole mind, and with thy whole strength." (Mark 12:30).