Encyclopedia of Mormonism, pg. 586; “The Savior’s reference to the “gates of hell” (Hades, or the spirit world; Matt. 16:18) indicates, among other things, that God’s priesthood power will penetrate hell and redeem the repentant spirits there. Many have been, and many more will yet be, delivered from hell through hearing, repenting, and obeying the gospel of Jesus Christ in the spirit world after the death of the body. LDS doctrine emphasizes that after his mortal death Jesus Christ went to the spirit world and organized the teaching of the gospel there (D&C 138; cf. Luke 23:43; 1 Pet. 3:18-20).”
John 8:21; “Then said Jesus again unto them, I go my way, and ye shall seek me, and shall die in your sins: whither I go, ye cannot come.”
What does 1st Peter have to do with Jesus defending His bride in Matthew 16?