When reading the letters to the 7 churches in Revelation chapters 2 and 3, Jesus evaluates then both warns and encourages with both rewards and punishments. Rewards are for those who obey, return and repent. Correction and punishment for those who do not obey and repent. Since the beginning of the Church Age many believers have died who were living in disobedience to God's will and not ready to meet Him as He would have preferred them to be. They are saved but will suffer the loss of a full-reward. Some will be barely saved as if plucked from the fire. The Rapture is an event which ends The Church Age and like death will expose who is ready or not. Heaven is a guarantee of salvation but the Rapture is not. A Bride is taken out from the Body of Christ - much like Eve was taken out from the body of Adam. Not all of the members of the Body of Christ are His Bride. We find this in parables that Jesus taught about - being ready, faithful service and being placed at The Banquet. Also, "The Bride makes herself ready" she is worthy to wear the jewels and the fine linen because of righteous deeds. There are believers within the Church who are not serving Christ, disobedient children and unrepentant. They will not be raptured (or loose their salvation) but must be "made ready" through the fires of Tribulation to prove that their faith is saving faith.
To preach then, that all who are believers will be taken up in the Rapture is to not understand both the justice and love of God. We reap what we sow and God disciplines and corrects all whom He calls to be His children. Jesus "will choose" for Himself a Bride those who choose Him first above all, those who are "filled" with the Holy Spirit, those who have heard and come out from the world and are "ready" when he calls them to come up here.