Whilst the Choir and people are being honoured with incense, the Priest washes his hands. This ceremony is marked, at this particular moment, because the Priest has just been using the Thurible, which always soils the hands, because of the smoke. But at the same time, this washing of the hands embodies a mystery: it expresses the necessity there is for the Priest to purify himself yet more and more, as he advances in the Holy Sacrifice. Just as Our Lord washed the feet of His Apostles before instituting the Holy Eucharist and giving them Holy Communion, so too, should the Priest purify himself. In the Ambrosian Liturgy, this rite of washing the hands takes place during the Canon, before the Consecration; the signification is ever the same, namely, the duty of self-purification incumbent on the Priest; nevertheless, the moment chosen for this rite by the Roman Church, ever discreet in all her decisions, is preferable to that adopted by the Ambrosian Liturgy.
To accompany this action, which signifies what the purity of the Priest should be, holy Church has selected the Psalm xxv., which is marked in the Monastic Office in the First Nocturn of Sunday’s Matins: Judica me, Domine, quoniam ego in innocentia mea ingressus sum. In this Psalm, it is Our Lord Himself who speaks; it is easy to perceive that the Priest could never apply such words to himself. Holy Church appoints but the half of this Psalm to be said, commencing with the words: Lavabo inter innocentes manus meas et circumdabo altare tuum, Domine, ... I will wash my hands, O Lord, and make myself like to those who are in the state of innocence, so as to be worthy to approach Thine Altar, to hear Thy sacred Canticles and to recount Thy marvellous Works. Every word is wonderfully adapted to the present occasion. Further on, we come across this other remarkable expression of the Prophet: Domine, dilexi decorem domus tuae et locum habitationis gloriae tuae: Lord, I have loved the beauty of Thy House, the Place where Thy Glory dwelleth. David here speaks of that Tabernacle under the shade of which he dwelt so happy, although the Temple was not yet in existence, for it was not built till Solomon’s time. The Psalm is continued to the end, so as to allow the Priest ample time for washing and wiping his hands. This other verse of the same Psalm: Ego autem in innocentia mea ingressus sum: I have walked in mine innocence, proves to us, once again, that this Psalm is altogether Messianic; the Priest, therefore, says it in the Name of Christ, with whom he is but one and the same, during the action of the Great Sacrifice. In Masses of the Dead, and at Passiontide (when the Mass is ferial), the Gloria Patri is omitted at the end of this Psalm. This omission of the Gloria in this place is always coupled with the omission of Psalm Judica at the beginning of the Mass.