noun
Specifically refers to a new convert or novice in the Catholic Church. Not a general term for a beginner.
彼は洗礼を受けて、修練者として教会に迎えられた。
He was baptized and welcomed into the church as a neophyte.
新信者 also means a new believer or convert, but 修練者 is more formal and specifically Catholic.
From 修練 (training, discipline) + 者 (person). The specific Catholic sense is a semantic borrowing.