Actually, the “seven deadly sins” are a reduced version of the Eight Grievous Vices catalogued by St. John Cassian in a brief work of the same title in the late fourth or early fifth century. The one omitted by St. Gregory the Dialogist was self-esteem. They also have parallels in the Ladder of Divine Ascent by St. John Climacus, a monk of St. Catherine’s Monastery in Sinai, a contemporary of St. Gregory, who is honored by the Orthodox with commemoration on one of the Sundays of Great Lent.
All of them (all eight, and the finer and more extensive list of vices St. John Climacus catalogs) can be seen to be sinful on the basis of Holy Scripture, but the cataloging of them and the understanding of the interrelations among different temptations as an aid to struggling against them with the help of God’s grace is part of the empirical experience of the Church, particularly of monastics.
It’s rather sad Pope Gregory omitted self-esteem, as the vice of self-esteem is now taught as if it were a virtue in our K-12 schools, and while our culture might objectively “celebrate” the other grievous vices, leaving aside fools who do so only for shock value and Randians who seem to think avarice is a virtue, no one has the temerity to actually teach that any of the seven deadly sins are virtuous.
I think I disagree about self-esteem. The way it’s taught or inculcated is dangerous nonsense. I would say there are self-esteem disorders in either extreme. But to esteem oneself as a redeemed sinner, precious in God’s sight is helpful to mental health.
I find it hard to believe that the modern notion of "self-esteem" even existed in Cassian's time, and surely he didn't write in present-day English! I don't recall encountering the phrase in anything written before the 60s, though it might have been a "term of art" in therapeutic circles before that. What is the Greek(?) word being translated as "self-esteem"?
He writes about what a subtle vice it is, how it finds an opening in the practice of any virtue (see how well I fast. . . see how humble I am. . . ).
We learned of this by the term "spiritual pride" (incidentally, there's a passage about it, I think under that name, in Eliot's Murder in the Cathedral.
You are better off sticking with the Bible. It is much more instructive.