Ephesians 4:30 - Grieve Not the Holy Spirit

 And grieve not the holy Spirit of God, whereby ye are sealed unto the day of redemption. -- Ephesians 4:30, King James Version.

Many trinitarians (and some others) may point to Ephesians 4:30 as proof that the Holy Spirit is a person. "God," however, in the expression, "the holy spirit of God", obviously is referring to only one person, and the "holy spirit" is presented as be a possession of that one person who is God. This is in harmony with Ephesians 4:6, where only the Father is presented as being  the "one God". Likewise in Ephesians 4:13, "God" is again presented as being only one person, and "Christ" (meaning the anointed) is distinguished from being that one person, since he is presented as being the son of that one person. 

The scriptures show that God's Holy Spirit is is likened to God's finger, at least in as God's Holy Spirit represents the power of God. (Matthew 12:28; Luke 11:20) One's finger is, of course, and extension of one's self, but one would not say that one's finger is another person of oneself. Regardless, what one's finger does is what is directed by the owner of that finger; what is done by one's finger is what is done by the person to whom the finger belongs. Likewise, with God and and His Holy Spirit. The point is that as one's finder is an extension of the person to whom the finger belongs, so God's Holy Spirit is an extension of God to whom the Holy Spirit belongs. God's Holy Spirit could be used as an extension of God as more or less figuratively being God's mouth, His eyes, His ears, His heart, His disposition, His will, etc. Of course, God's Holy Spirit, being an extension of God Himself, could certainly be spoken of as as being grieved. This does not mean that we need to imagine, assume, add to, and read into the scriptures that God is three persons, and that His Holy Spirit is one of the persons of Himself.

Because of their desire to make God's Holy Spirit appear to be a person, many translations add a personal pronoun to the Bible in this verse (and many other verses pertaining to the Holy Spirit). For instance, the New King James Version adds the pronoun "whom":

And do not grieve the Holy Spirit of God, by whom you were sealed for the day of redemption.

In the Greek, the word for spirit is neuter, and thus, in harmony with the Koine Greek syntax, all pronouns relating to spirit are neuter. IF the spirit were referring to a person, it could still be neuter in the Greek.  One cannot depend on the gender of pronouns in the Koine Greek to determine whether an object is referring to a person or not. Thus, supplying the pronoun "whom" in an English translation does not mean that we need to imagine and assume the God's Holy Spirit is actually a "him", a masculine person. There is certainly no reason to add to what Paul wrote anywhere in Ephesians 4 that the God of Abraham, Isaac and Jacob is three persons, and that one those persons is God's Holy Spirit.