From the early days of Western Christianity, Pentecost became one of the days set aside to celebrate Baptism. In Northern Europe Pentecost was preferred even over Easter for this rite, as the temperatures in late spring might be supposed to be more conducive to outdoor immersion as was then the practice. It is proposed that the term Whit Sunday derives from the custom of the newly baptized wearing white clothing, and from the white vestments worn by the clergy in English liturgical uses. The holiday was also one of the three days each year (along with Christmas and Easter) Roman Catholics were required to confess and receive Holy Communion in order to remain in good ecclesiastical standing.