In earlier times, the rite which gives the day its name – the sprinkling of ash on the heads of penitents – was reserved to those public penitents who underwent a public and dramatic expulsion from the church building. Although no longer generally practiced, echoes of the above can be found in today’s Liturgy, which contains a general imposition of Ashes on all of those who wish to receive them. Public penitents assembled in sack-cloth in their bare feet and were given a penance for Lent and then were given ashes, which the bishop had blessed. Then followed a ceremony that included the Seven Penitential Psalms and Litany. It culminated in the penitents being led, physically, from the church and expelled. Then, on Holy Thursday, after forty days of penance, they were reconciled.
The Penitential Psalms were generally used at the beginning of Lent, at the ceremony by which the public penitents were symbolically expelled from the church, and again on Holy Thursday, when they were brought back in. The Penitential Psalms are Ps 6, Ps 31(32), Ps 37(38), Ps 50 (51), Ps 101 (102), Ps 129 (130), and Ps 142 (143). The Hebrew numbering are in parentheses; the Hebrew Bible counted the psalms one way while the Septuagint translation of the Hebrew Bible into Greek counted many psalms slightly differently. The early Christians used the Greek Septuagint, and then went on to translate that version into Latin (or the Vulgate) following the Septuagint numbering.