Sing the Te Deum in thanksgiving for the past year and the Veni Creator for new year, and gain a
plenary indulgence.
In the Enchiridion Indulgentiarum, 4th edition, 26:
§ 1. A plenary indulgence is granted to the Christian faithful who, in a
church or in an oratory, are present [take part] in a recitation or solemn
chant of: …1° the hymn Veni Creator … on the first day of the year, imploring divine assistance for the whole of the coming year…
2° the Te Deum hymn, on the last day of the year, in
thanksgiving to God for the favors received in the course of the entire year.
