Well, to answer the question one should automatically know they need to go to the Book of Revelation and read what Jesus said to those two Churches of Smyrna and Philadelphia. That ought to be the first step...
Rev 2:8-11
8 And unto the angel of the church in Smyrna write; "These things saith the first and the last, which was dead, and is alive;
That of course is Lord Jesus speaking, He is "the first and the last, which was dead, and is alive:".
9 I know thy works, and tribulation, and poverty, (but thou art rich) and I know the blasphemy of them which say they are Jews, and are not, but are the synagogue of Satan.
10 Fear none of those things which thou shalt suffer: behold, the devil shall cast some of you into prison, that ye may be tried; and ye shall have tribulation ten days: be thou faithful unto death, and I will give thee a crown of life.
11 He that hath an ear, let him hear what the Spirit saith unto the churches; He that overcometh shall not be hurt of the second death.
KJV
And to the Church of Philadelphia...
Rev 3:7-11
7 And to the angel of the church in Philadelphia write; These things saith He That is holy, He That is true, He That hath the key of David, He That openeth, and no man shutteth; and shutteth, and no man openeth;
8 I know thy works: behold, I have set before thee an open door, and no man can shut it: for thou hast a little strength, and hast kept my word, and hast not denied my name.
The idea of that "key of David" is about those of His servants that are 'sealed' by The Holy Spirit because they have kept His Word, and not denied Him. Because of that no man can close that symbolic door of the "strong meat" of His Word. Nor can those not sealed open it.
And here is one of the "strong meat" matters which only those two sealed Churches of Smyrna and Philadelphia had which the other five Churches did not...
9 Behold, I will make them of the synagogue of Satan, which say they are Jews, and are not, but do lie; behold, I will make them to come and worship before thy feet, and to know that I have loved thee.
10 Because thou hast kept the word of My patience, I also will keep thee from the hour of temptation, which shall come upon all the world, to try them that dwell upon the earth.
The "hour of temptation" is about the time of "great tribulation" when the "strong delusion" of 2 Thess.2 is to occur. It's about the coming Antichrist/false-Messiah to Jerusalem to work great signs, wonders, and miracles that will deceive the whole world into believing he is God, except Christ's elect here represented by these 'two candlesticks.'
How will these sealed elect servants of Christ be kept from that hour of temptation? by being raptured to escape it? NO! by their being 'sealed' with God's seal to go through it, having that "key of David" so they cannot be deceived by Satan and his host.
11 Behold, I come quickly: hold that fast which thou hast, that no man take thy crown.
KJV
