Complex sentence: The Society of the Holy Cross is an Anglo-Catholic order of priests in the Anglican tradition, not to be confused with the Roman Catholic Priestly Society of the Holy Cross which is an order of Opus Dei priests.
Split into simpler sentences: The Society of the Holy Cross is an Anglo-Catholic society for priests in the Anglican tradition. It ought not be confused with the Roman Catholic Priestly Society of the Holy Cross which is an order of Opus Dei priests.