"Jesus Christ promised to preserve the Church from error. If His prediction and promises were false, then he would not be God, since God cannot lie. Christ said: 'Thou art Peter, and upon this rock I will build My Church, and the gates of hell shall not prevail against it' If therefore the Church falls into error, the gates of hell certainly would prevail against it." (My Catholic Faith, p. 144).
"Our Blessed Lord, in constituting St. Peter Prince of His Apostles, says to him: 'Thou art Peter, and upon this rock I will build My Church, and the gates of hell shall not prevail against it.' Christ makes here a solemn prediction that no error shall ever invade His Church, and if she fell into error the gates of hell certainly prevailed against her." (The Faith of Our Fathers, p. 55).
The Expository Dictionary of New Testament Words, by W.E. Vine defined the word "hell" of
Matt. 16:18 as, "HADES, the region of departed spirits of the lost (but including the blessed dead
in periods preceding the Ascension of Christ)." (p. 187). Mr. Vine on page 188 added, "The word
is used four times in the Gospels, and always by the Lord, Matt. 11:23; 16:18; Luke 10:15; 16:23;
it is used with reference to the soul of Christ, Acts 2:27,31; Christ declares that He has the keys
of it, Rev. 1:18..." The Theological Word Book of the Bible, edited by Alan Richardson, says of
the word, "The name for this region was SHEOL (Heb.) or HADES (Gk.)...It was in Sheol that a
man was 'gathered to his fathers'; the dead may not return to earth, but the living must eventually
go to them (cf. II Sam. 12:23)." (p. 106).
When Jesus said, "...Upon this rock I will build my church, and the gates of hell shall not prevail
against it," He did not promise to preserve the church from error. He simply meant that the gates
of hell would not prevail against Him in preventing Him from building His church. Acts 2:31-32
says, "...He, foreseeing it, spoke of the resurrection of the Christ. For neither was He abandoned
to hell, nor did His flesh undergo decay. This Jesus God has raised up, and we are all witnesses of
it." Hence, Jesus was not stopped from building His church by being left in hell ("hades" in the
Greek, meaning the place of the disembodied spirits) because His spirit was again reunited with
His body. If He had been confined to hades, it would have prevailed against Him.
A parallel constructed sentence to Matt. 16:18 is, "The students are going near the swamp, and the faculty does not like it." The faculty does not like what--the students? No, the faculty does not like the students going near the swamp. Jesus said, "...I will build my church and the gates of hell shall not prevail against it." The gates of hell shall not prevail against what? They would not prevail against Christ building His church.