The Triduum is an excellent example that the law of belief and doctrine is founded upon the law of prayer and worship (lex orandi, lex credendi). Let me explain. The Catholic Church teaches that the services of Holy Thursday, Good Friday, and Saturday’s Easter Vigil are not to be considered as three different Masses but rather as one Mass.
Note that, in honor of ancient Israel where a day begins and ends at sunset, we start the Mass before sunset on Thursday.
Thursday’s service includes the foot-washing ceremony, signifying the basis of leadership within the Church, and concludes with Eucharistic adoration in remembrance of our Lord’s prayer in the garden of Gethsemane.
On Friday, we remember the actual cruxifixion with the Stations of the Cross at 3pm and then at the Good Friday service at 7pm we venerate the cross, celebrating the glorious work of God for our salvation. As Saint Paul says, “Christ, and Him crucified”.
On Saturday, we begin the Easter Vigil at 8:30pm so that the Mass will not conclude until after sunset, i.e. on Sunday morning according to traditional timekeeping, as we celebrate our Lord’s resurrection ‘on the third day’ and welcome new catechumens into the Church.
Thus the Church keeps together in one celebration, in one Mass, the interrelated events which various groups outside the fullness of the Catholic Church sometimes have a tendency to separate, giving undue significance to one component or another.
The Triduum is the highpoint of our liturgical year and so the several Masses on Easter Sunday are a reflection of this, not so much anticlimactic as an aesthetically proper easing at the conclusion of the drama of the work of God for us.