"What" are the keys mentioned in Matthew 16:19?
My answer is, they are the sacraments.
God be gracious to me a sinner?
Ya won't like it, but I'll tell you anyway.
When Jesus said that He would give them the keys of the kingdom.
He did not just randomly make the statement.
What He said was on the same subject that He had been discussing with them when He ask "but whom say ye that I am?"
Matt 16:15-20
15 He saith unto them, But whom say ye that I am?
Simon Peter answered.
16 And Simon Peter answered and said, Thou art the Christ, the Son of the living God.
Then Jesus said that Simon Barjona did not get that wisdom or understanding from men's understanding.
Jesus said that that knowledge was revealed to Simon by God.
17 And Jesus answered and said unto him, Blessed art thou, Simon Barjona: for flesh and blood hath not revealed it unto thee, but my Father which is in heaven.
18 And I say also unto thee, That thou art Peter, and upon this rock I will build my church; and the gates of hell shall not prevail against it.
19 And I will give unto thee the keys of the kingdom of heaven: and whatsoever thou shalt bind on earth shall be bound in heaven: and whatsoever thou shalt loose on earth shall be loosed in heaven.
The "rock" as well as the keys are the same thing!
Knowledge that is revealed to man by the Holy Spirit of God, The Father.
The church is built on that revelation knowledge. Without the revelation of God's Word to man the "church", which consist of born again people would not have the knowledge and understanding to resist the devil and make the devil flee.
The revealing of God's Word to man gives man the keys of the kingdom.
The keys are the knowledge and understanding of how the kingdom operates.
Without that knowledge we could not bind anything cause we would not know how or what to bind and what to loose.
Then Jesus made a another statement concerning the subject He was speaking to them on.
The Holy Spirit revealed to Peter that Jesus was the Christ, The Son of God.
Jesus told them not to share that revelation with anyone.
20 Then charged he his disciples that they should tell no man that he was Jesus the Christ. KJV
