Josquin Desprez's setting of Psalm 129 (De profundis). This Septuagesima Sunday's tract is taken from the same Psalm. Josquin's polyphonic setting evokes the penitential spirit of the Psalm.
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From DRBO.ORG:
De profundis. A prayer of a sinner, trusting in the mercies of God. The sixth penitential psalm.
[1] Out of the depths I have cried to thee, O Lord:
Canticuм graduum. De profundis clamavi ad te, Domine;
[2] Lord, hear my voice. Let thy ears be attentive to the voice of my supplication.
Domine, exaudi vocem meam. Fiant aures tuae intendentes in vocem deprecationis meae.
[3] If thou, O Lord, wilt mark iniquities: Lord, who shall stand it.
Si iniquitates observaveris, Domine, Domine, quis sustinebit?
[4] For with thee there is merciful forgiveness: and by reason of thy law, I have waited for thee, O Lord. My soul hath relied on his word:
Quia apud te propitiatio est; et propter legem tuam sustinui te, Domine. Sustinuit anima mea in verbo ejus;
[5] My soul hath hoped in the Lord.
Speravit anima mea in Domino.
[6] From the morning watch even until night, let Israel hope in the Lord.
A custodia matutina usque ad noctem, speret Israel in Domino;
[7] Because with the Lord there is mercy: and with him plentiful redemption.
Quia apud Dominum misericordia, et copiosa apud eum redemptio.
[8] And he shall redeem Israel from all his iniquities.
Et ipse redimet Israel ex omnibus iniquitatibus ejus.
http://drbo.org/drl/chapter/21129.htm