Again, stop shortchanging Jesus' words in MATTHEW 16:18-19. Jesus gave the KEYS TO THE KINGDOM TO PETER. If the church is not a kingdom, then Jesus' is in error or in a bipolar disorder. Stop side stepping this simple verse. Assembly is the literal meaning of church in Greek but that word is already transliterated in broader terms, just like the word "bible", "eucharist", "catholic", baptism etc. 2ND, Never did the church declared that the kingdom of God is "only" a worldly kingdom. The kingdom of God rules in heaven and earth because Jesus was victorious on the cross to establish his New Covenant among the human race.
Peter has the Keys of Authority over the Earthly Kingdom, the Church
2 Sam. 7:16; Psalm 89:3-4; 1 Chron.17:12,14 - God promises to establish the Davidic kingdom forever on earth.
Matt. 1:1 - Matthew clearly establishes this tie of David to Jesus. Jesus is the new King of the new House of David, and the King will assign a chief steward to rule over the house while the King is in heaven.
Luke 1:32 - the archangel Gabriel announces to Mary that her Son would be given "the throne of His father David."
Matt. 16:19 - Jesus gives Peter the "keys of the kingdom of heaven." While most Protestants argue that the kingdom of heaven Jesus was talking about is the eternal state of glory (as if Peter is up in heaven letting people in), the kingdom of heaven Jesus is speaking of actually refers to the Church on earth. In using the term "keys," Jesus was referencing Isaiah 22 (which is the only place in the Bible where keys are used in the context of a kingdom).
Isaiah 22:22 - in the old Davidic kingdom, there were royal ministers who conducted the liturgical worship and bound the people in teaching and doctrine. But there was also a Prime Minister or chief steward of the kingdom who held the keys. Jesus gives Peter these keys to His earthly kingdom, the Church. This representative has decision-making authority over the people - when he shuts, no one opens. See also Job 12:14.
Rev. 1:18; 3:7; 9:1; 20:1 - Jesus' "keys" undeniably represent authority. By using the word "keys," Jesus gives Peter authority on earth over the new Davidic kingdom, and this was not seriously questioned by anyone until the Protestant reformation 1,500 years later after Peter’s investiture.
Matt. 16:19 - whatever Peter binds or looses on earth is bound or loosed in heaven / when the Prime Minister to the King opens, no one shuts. This "binding and loosing" authority allows the keeper of the keys to establish "halakah," or rules of conduct for the members of the kingdom he serves. Peter's "keys" fit into the "gates" of Hades which also represent Peter’s pastoral authority over souls.
Matt. 23:2-4 - the "binding and loosing" terminology used by Jesus was understood by the Jewish people. For example, Jesus said that the Pharisees "bind" heavy burdens but won't move ("loose") them with their fingers. Peter and the apostles have the new binding and loosing authority over the Church of the New Covenant.
Matt. 13:24-52 -Jesus comparing the kingdom of heaven to a field, a mustard seed, leaven, and a net demonstrate that the kingdom Jesus is talking about is the universal Church on earth, not the eternal state of glory. Therefore, the keys to the "kingdom of heaven" refers to the authority over the earthly Church.
Matt. 25:1-2 - Jesus comparing the kingdom of heaven to ten maidens, five of whom were foolish, further shows that the kingdom is the Church on earth. This kingdom cannot refer to the heavenly kingdom because there are no fools in heaven!
Mark 4:26-32 - again, the "kingdom of God" is like the seed which grows and develops. The heavenly kingdom is eternal, so the kingdom to which Peter holds the keys of authority is the earthly Church.
Luke 9:27 - Jesus says that there are some standing here who will not taste death until they see the "kingdom of God." This kingdom refers to the earthly kingdom of Christ, which Jesus established by His death and resurrection on earth.
Luke 13:19-20 - again, Jesus says the kingdom of God is like a mustard seed which grew into a tree. This refers to the earthly Church which develops over time, from an acorn to an oak tree (not the heavenly state of glory which is boundless and infinite).
Matt 12:28; Mark 1:15; Luke 11:20; 17:21 - these verses provide more examples of the " kingdom of God" as the kingdom on earth which is in our midst.
1 Chron. 28:5 - Solomon sits on the throne of the kingdom of the Lord. This shows that the "kingdom of God" usually means an earthly kingdom.
1 Chron. 29:23 - Solomon sits on the throne of the Lord as king in place of King David. The throne of God refers to the earthly kingdom.
Matt. 16:19 - Peter holds keys to this new Davidic kingdom and rules while the real King of David (Jesus) is in heaven.
Luke 12:41-42 - when Peter asks Jesus if the parable of the master and the kingdom was meant just for the apostles or for all people, Jesus rhetorically confirms to Peter that Peter is the chief steward over the Master's household of God. "Who then, (Peter) is that faithful and wise steward whom his master will make ruler over His household..?"
Ezek. 37:24-25 - David shall be king over them forever and they will have one shepherd. Jesus is our King, and Peter is our earthly shepherd.