Who holds back the forces of Satan until the tribulation starts?
The Holy Spirit is the hinderer who restrains the forces of Satan until the appointed time of the tribulation. He dwells in every believer, and through the believer and His indwelling presence, God places a brake on the earth against the influx of evil until that restraint is taken out of the way.
Les explains that the one who now hindereth will hinder until he, that hinderer, is taken out of the way. The person with power today to hold back the forces of Satan like a dam on a river, so things will not break loose and start bringing in the tribulation until the right time, is the Holy Spirit. The Holy Spirit dwells today in every believer, in the heart and life of every believer. Thus the only break God has on the earth against the influx of all this evil work is the believer and the indwelling Holy Spirit. That is God's break on the system, which is why believers must know the Book, know what they believe, and stand on it.
For the mystery of iniquity doth already work: only he who now letteth will let, until he be taken out of the way.