Why is it that in both the Bible and the writings of the Apostolic Fathers the Holy Spirit seems less emphasized than the Father and the Son?
For example, in the beginning of all of St. Paul's Epistles he salutes the Churches in the name of God the Father and the Lord Jesus Christ, but never mentions the Holy Spirit. The same rule applies to the beginning lines of the Epistle of St. Polycarp to the Philippians (his only surviving work), the Epistles of St. Ignatius, the Epistle of St. Clement to the Corinthians, etc.
There are also many portions in Scripture where the roles of the Father and the Son are emphasized, but the Spirit is not mentioned. For example John 17:3, 2 John 1:9, John 5:23, etc.
Is there a particular reason this is the case? It just seemed odd to me that the third coequal person of the All-Holy Trinity is (potentially) undermined in these works compared to the Father and Son.