According to John Welch, the Greek word translated into English as "perfect" in Matthew 5:48 (compare 3 Nephi 12:48) is teleios. This important word is used in Greek religious literature to describe the person who has become fully initiated in the rituals of the religion. Teleios is "a technical term of the mystery religions, which refers to one initiated into the mystic rites, the initiate. The word is used in Hebrews 5:14-6:1 to distinguish between the initial teachings and the full instruction; and in Hebrews 9:11 it refers to the heavenly temple. Generally in the Epistle to the Hebrews, its usage follows a "special use" from Hellenistic Judaism, where the word teleioo means "to put someone in the position in which he can come, or stand, before God." Thus, in ritual connotations, this word refers to preparing a person to be presented to come before God "in priestly action" or "to qualify for the cultus." Early Christians continued to use this word in this way in connection with their sacraments and ordinances.
Most intriguing in this regard is the letter of Clement of Alexandria describing the existence (c. 200 A.D.) of a second Gospel of Mark, reporting the Lord's doing as recounted by Peter and going beyond the public Gospel of Mark now found in the New Testament. This so-called Secret Gospel of Mark according to Clement, contained things "for the use of those who were being perfected (teleioumenon). Nevertheless, he [Mark] did not divulge the things not to be uttered, nor did he write down the hierphantic [priesthood] teaching of the Lord . . . The copy was read "only to those who are being initiated into the great mysteries." [John W. Welch, The Sermon at the Temple and the Sermon on the Mount, F.A.R.M.S., pp. 58-59]
Thus, the temple setting in the Book of Mormon more fully amplifies this sacred covenant concept than the Bible does.