“Five times does the priest turn round towards the people [in the Traditional Latin Mass], to denote that our Lord manifested Himself five times on the day of His resurrection, as stated above in the treatise on Christ’s resurrection (Q55,A3,OBJ 3). But the priest greets the people seven times, namely, five times, by turning round to the people, and twice without turning round, namely, when he says, ‘The Lord be with you’ before the Preface, and again when he says, ‘May the peace of the Lord be ever with you’: and this is to denote the sevenfold grace of the Holy Ghost. But a bishop, when he celebrates on festival days, in his first greeting says, ‘Peace be to you,’ which was our Lord’s greeting after resurrection, whose person the bishop chiefly represents.”   -  St. Thomas Aquinas