Acts 2:4 (ESV) … “And they were all filled with the Holy Spirit and began to speak in other tongues as the Spirit gave them utterance.”
The filling of the Spirit has to do with power for witness and service (Acts 1:8). We are not exhorted to be baptized by the Spirit, for this is something God does once and for all when we trust His Son. But we are commanded to be filled with the Spirit (Eph. 5:18), for we need His power constantly if we are to serve God effectively. At Pentecost, the Christians were filled with the Spirit and experienced the baptism of the Spirit; but after that, they experienced many fillings (Acts 4:8, 31; 9:17; 13:9) but no more baptisms.
Occasionally someone says, “What difference does it make what words we use? The important thing is that we have the experience!” I doubt that they would apply that same approach to any other area of life such as medicine, cooking, or mechanics. What difference does it make if the pharmacist uses arsenic or aspirin in the prescription, just so long as you get well? Or if the mechanic installs an alternator or a carburetor, just so long as the car works?
The Holy Spirit has revealed God’s truth to us in words (1 Cor. 2:12–13), and these words have definite meanings that must not be changed. Regeneration must not be confused with justification, nor propitiation with adoption. Each of these words is important in God’s plan of salvation and must be defined accurately and used carefully.
The baptism of the Spirit means that I belong to His body; the fullness of the Spirit means that my body belongs to Him. The baptism is final; the fullness is repeated as we trust God for new power to witness. The baptism involves all other believers, for it makes us one in the body of Christ (Eph. 4:1–6); while the fullness is personal and individual. These are two distinct experiences and they must not be confused.