MANDATUM NOVUM – a new commandment was given: “that you love one another as I have loved you” (John 13.34). And though we have heard it, and though we believe in the sense of it, and though we would love one another, and though we need to be loved, yet in innumerable ways the commandment remains unfulfilled. We are in perpetual need of Grace. And so, on Maundy Thursday, Trisagion is prayed. The Trisagion prayer is considered one of the oldest prayers in Christianity. It may be that the prayer was originally an expansion of the angelic cry recorded in Revelation 4.8
Άγιος ο Θεός, άγιος ισχυρός, άγιος αθάνατος ελέησον ημάς.
Holy God, holy and strong, holy and immortal, have mercy upon us.