From the St Andrew's Daily Missal
The Septuagesima season forms a remote preparation for Easter and Lent a proximate one; its last two weeks known as Passiontide, being an immediate preparation for the Feast.
The celebrations and ceremonies of the last week, known as the Great Week or Holy Week, have their origin in the Church at Jerusalem. There, with the Holy Gospels in hand, the Christians would follow their Redeemer step by step, piously gathering on the very spot precious souvenirs of the most solemn among all events, that which marked the close of His mortal life.
These celebrations, at first local in character, were adopted into the liturgy at Rome, where the very churches were planned in such a manner, us to make it possible to carry out the offices of Holy Week in the way that had been customary at Jerusalem. The last three days are called the Sacred Triduum. During this fortnight the Church suppresses the psalm Judica and in several instances the Gloria Patri also, since these had no place in the ancient Liturgy. Moreover, she veils all pictures and statues.
With regard to this, certainly devotion to the saints should yield before the great work of Redemption, but when it is observed that the crucifix itself is veiled, we see here a trace of the custom which obtained of suspending a curtain between the sanctuary and the nave, during the whole of Lent. In those times public penitents who had been excluded from the Church could not enter it again until Holy Thursday, and when this custom was abolished, all Christians were more or less placed in the position of such penitents. Although no sentence of exclusion was pronounced against them, the sanctuary and all that took place there was hidden from them, to show that they could only merit the share in Eucharistic worship given them in their Easter Communion, after they had brought forth fruits worthy of penance.
Finally, by stripping the altars and silencing all bells and organs on Holy Thursday, Good Friday and Holy Saturday, the Church gives expression to the grief which she feels at the memory of the death of her divine Spouse.
Note: The St Andrew's Daily Missal, 1945 edition - probably the best Latin-English handmissal ever - has been reprinted by St Bonaventure Press. Every traditional Catholic home should have one! http://www.libers.com/sam.htm