The Introit (Entrance Antiphon) or Hymn

If the given antiphon is not used, as in many Masses with music, then the substituted hymn accompanies the procession. Weekday Masses frequently have the Introit recited, either by the congregation as the priest approaches the altar or by the priest after he has made the sign of the cross and extended the greeting. Given that the prayer book of the Jews becomes that of the early Christians, there can be no doubt that the psalms were employed for singing at the beginning of the liturgy. The text of the antiphon varies with the season and type of celebration. The Eastern rites by comparison do not include an Introit because there is no procession to the altar. Their ritual begins in the sanctuary. The Western rite ordinarily begins outside the sanctuary with a procession. The old ritual also included fixed prayers at the foot of the altar which arguably complemented the true variable Introit. Indeed, the old Judica Me prayer is currently the actual Introit for the Mass of the Fifth Sunday of Lent:

Give me justice, O God, and plead my cause against a nation that is faithless. From the deceitful and cunning rescue me, for you, O God, are my strength.