Our initial response would be to see both days as beginnings, the 1st of January being the beginning of the Gregorian New Year and Pentecost being the beginning or birthday of the Church. Most people are unaware that these common associations are actually inaccurate – that is until the Middle Ages, the 25th of March or the Feast of the Annunciation was New Year’s Day and that it would be more theologically correct to speak of the birth of the Church from the wounds of Christ on Good Friday.
The correct answer to the above question is the Holy Spirit who is invoked in a special way on both days in the form of an ancient hymn 𝐕𝐞𝐧𝐢 𝐂𝐫𝐞𝐚𝐭𝐨𝐫 𝐒𝐩𝐢𝐫𝐢𝐭𝐮𝐬.
If the 𝐓𝐞 𝐃𝐞𝐮𝐦 was the hymn of thanksgiving which closes the end of the previous year, 𝐕𝐞𝐧𝐢 𝐂𝐫𝐞𝐚𝐭𝐨𝐫 𝐒𝐩𝐢𝐫𝐢𝐭𝐮𝐬 is the hymn which welcomes the Spirit at the beginning of the New Year.
The hymn 𝐕𝐞𝐧𝐢 𝐂𝐫𝐞𝐚𝐭𝐨𝐫 𝐒𝐩𝐢𝐫𝐢𝐭𝐮𝐬 was probably written by Rabanus Maurus (856), Archbishop of Mainz, and has been widely used from the end of the tenth century on. In addition to its place in the Pentecost liturgy, the Veni Creator has also been assigned as the official opening prayer for Church councils and synods. It is recited and sung by the faithful all over the world at the start of important undertakings, such as the beginning of a school year, at conventions, missions, retreats, and on many similar occasions.