What is the difference between the indwelling of the Holy Spirit and the filling of the Holy Spirit?

The indwelling and the filling of the Holy Spirit are not the same. At the moment of salvation every believer is indwelt by the Spirit; this is once-for-all, and it cannot be changed or lost—He indwells every believer all the time. But with the indwelling an inner conflict begins between the Spirit and our old sin nature, and our volition is the arbiter, deciding moment by moment who controls our soul. The filling is therefore a matter of choice: we are commanded to be filled, we lose it by grieving or quenching the Spirit through sin or apathy, and we regain it through confession. There is no spiritual life apart from the indwelling, and no spiritual production apart from the filling.