It celebrates 56 days before Holy Easter.
The third Sunday of the Triod is dedicated to the most terrible event in human history, the coming Judgment. The remembrance of the terrible coming Judgment at the beginning of the Triod is necessary, because the ultimate purpose of all our spiritual struggle is to find ourselves at the right hand of the Despot Christ, during the great Judgment. This is well captured in the wonderful hymn of the day.
The holy hymn writers composed very instructive tropes, which exhort the faithful to feel the coming sure and terrible Judgment. In one of them we sing: “Remembering the awesomeness of your creation and your ineffable glory, I cry out, Lord, even with trembling fear I cry out” On earth when you come, judge, Christ, the universes, God after glory, then evil, from all kinds of punishment, from your right hand, Despot, you set me up”.