Baptism:  Is the baptism of the Holy Spirit
 a command or promise?

In Acts 1:2-5 it reads, "Until the day in which he (Christ) was taken up, after that he through the Holy Ghost had given commandments unto the apostles whom he had chosen: To whom (apostles) also he showed himself alive after his passion by many infallible proofs, being seen of them (apostles) forty days, and speaking of the things pertaining to the kingdom of God: And, being assembled together with them (apostles), commanded them (apostles) that they (apostles) should not depart from Jerusalem, but wait for the promise of the Father, which, saith he, ye (apostles) have heard of me. For John truly baptized with water; but ye (apostles) shall be baptized with the Holy Ghost not many days hence". In this text Christ is talking to the apostles and the baptism of the Holy Spirit is a promise that pertains to the apostles only. This is further evident in Acts 1:8, 9 which reads, "But  ye (apostles) shall receive power, after that the Holy Ghost is come upon you (apostles): and ye (apostles) shall be witnesses unto me both in Jerusalem, and in all Judaea, and in Samaria, and unto the uttermost part of the earth. And when he had spoken these things, while they (apostles) beheld, he was taken up; and a cloud received him out of their (apostles') sight."

The baptism of the Holy Spirit in this text was a promise limited only to the apostles. Notice verse 9 of Acts 2 says that the Apostles who would be baptized with the Holy Spirit, would "receive power". Who received power on Pentecost, Acts 2 ? The apostles did.  This power was demonstrated by the apostles being able to speak in tongues (languages).  But some in the crowd said "These men (apostles) are full of new wine" Acts 2:13. Peter then stood up with the eleven (apostles) and said in verse 15, "For these (apostles) are not drunken, as ye suppose, seeing it is but the third hour of the day".

The conclusion is this:  The promise concerning the baptism of the Holy Spirit has been fulfilled. It pertained to the apostles as noted in the scriptures above. Thus, the "one baptism" mentioned in Eph. 4:5 is not the Holy Spirit baptism, but the baptism of the great commission, Matt. 28:19, Mark 16:15-16 of which all men are subject to. The Ethiopian eunuch was obedient to that "one baptism" when as Acts 8:38 says, "they went down both into the water, both Philip and the eunuch; and he baptized him" The eunuch submitted to the only baptism that is valid today in the Christian age.