To be filled with the Holy Spirit is to be filled with one who is already there, in our hearts. Take up a sponge and while it is in your hand squeeze it. In that condition, plunge it in water and submerge it, keeping it in there. It is now in the water and the water is in it. As you hold it in the water, you open your hand, and as you do so the water fills all the pores which you release in this way. It is now filled with the water. When we receive Christ we are born anew and put into that sphere where the Holy Spirit is operating and the Holy Spirit comes to reside in us!