Once upon a time it was the tradition to cover all crucifixes, statues, and pictures in purple cloth from two Sundays before Easter until Good Friday. Those were the days when the Fifth Sunday of Lent, one week before Palm Sunday, was called Passion Sunday or Judica Sunday after the first word of the introit  "Judge me, O Lord..." (from Psalm 43).  The veiling referred to the closing words of the Sunday's gospel, "They picked up stones to throw at him, but Jesus hid himself, and went out of the temple" (John 8:59)  The Lenten veil also expressed the sorrow of the Church at this time. As a matter of fact, the Roman Missal still says in a note about the Saturday of the fourth week of Lent, that this tradition may be observed, continuing the veiling until the beginning of the vigil. Also, the unveiling of the cross prior to veneration on Good Friday is still an optional part of the liturgy.