Encyclopedia of Mormonism, pg. 103; “In harmony with biblical precedent and latter-day commandment, all saving and exalting ordinances, from baptism to temple marriage, are performed in the presence of witnesses, and a proper and faithful record is made and kept in the archives of the Church (2 Cor. 13:1; cf. D&C 128:2-5). Thus, ordinances become “a law on earth and in heaven” and, unless the covenants are violated, they cannot be annulled, “according to the decrees of the great Jehovah” (D&C 128:6-10).”

2 Corinthians 13:1; “This is the third time I am coming to you. In the mouth of two or three witnesses shall every word be established.”

Well…the passage from 2^nd Corinthians has absolutely nothing to do with getting married in the temple or being baptized for dead people.  In this passage Paul was exhorting the Corinthians to behave and call sinners to repentance in the presence of two or three witnesses.