Ephesians 2:18 is one of the clearest affirmations of the Trinity. It is quite difficult to understand one person simultaneously filling these three roles. We affirm what the Bible teaches: God in three persons, God in perfect unity.
For through him we both have access in one Spirit to the Father (Eph 2:18 ESV).
Our first question is who is the “him” through whom we have access? He is the crucified preacher (see verses 16 and 17). This is God the Son. The Spirit and the Father are obvious. Notice how the three persons of the Trinity work together in unity.
The Son provides access to the Father. Jesus gives us forgiveness, righteousness, and the rights of a first-born son. We receive these gifts by faith. The Spirit is the means by which we have access to the Father who is spirit. Our worship, our enjoyment of God, must be in spirit and in truth (John 4:24). The Son contributes his person to us, the Spirit contributes his person to us, and all of this is for access to the Father. The Father’s Son and the Father’s Spirit adamantly want us to know and be with the Father. Looking back into Ephesians 1, we see that the Father has planned this very thing (Eph 1:4-5). The persons of the Godhead are not separate phases of redemption existing individually or apart from the others. The persons of the Godhead are simultaneously existing in perfect unity and inviting us to come and be reconciled to God.