The side chambers signify the unsearchable riches of Christ becoming His extension as His fullness (1 Kings 6:5c). As believers in Christ, we are the temple and we are also the side chambers, the extension of Christ as His fullness.
The side chambers were in three stories, signifying being in the Triune God and in Christ's resurrection (v. 6).
The width of the first story was five cubits; the second, six cubits; and the third, seven cubits (v. 6). This signifies that the higher the church as Christ's fullness goes, the wider it is.
The door of the side chambers signifies the communication, the fellowship, of the church as the fullness of Christ (v. 8a). The side chambers were separate, but there was a door for communication. If there had been no door, that would have indicated autonomy. Today, some local churches either have no doors or they close their doors. They cut off fellowship between the churches. The wider the door, the richer the fellowship. Hence, all the local churches as chambers of Christ should widen their doors.
The winding stairs signify that the way to get into the church as the fullness of Christ is spiral without corners (v. 8b). This indicates that the fellowship between the churches should not have corners. Rather, the fellowship should continue to go up and up by a spiral stairway, like the street in the New Jerusalem (Rev. 22:1). In the New Jerusalem, from the mount where God's throne is, a river flows down the street in the form of a spiral to reach all the twelve gates.
The temple's two bronze pillars signify the Christ judged by God becoming the supporting strength of God's dwelling on the earth (1 Kings 7:15-22).