Following from here... (on Acts 2:1–11; Jn.7:37–52; 8:12).
The salvific rule that the Apostle Paul commands all the faithful to keep: Be kindly affectioned one to another with brotherly love; in honour preferring one another (Rm. 12:10)—is perfectly performed between the Hypostases of the Holy Trinity.
Each one of the Hypostases strives to prefer one another in honor; so also does each wish to decrease Himself before the Other Two.
And if each Hypostasis did not have that most sweet and holy striving to render His honor to the Other Two and decrease Himself in obedience, then in that endless love, which Each of them has for Each Other, the Trinitarian nature of the Divinity would drown in a kind of indifference of Hypostasis.
Thus, according to the boundless love of God the Spirit for God the Son, the Holy Spirit with boundless obedience hastened to fulfill the Son’s will and descended at the predetermined time upon the apostles.
God the Son firmly knew that God the Spirit would obey Him, and therefore He so firmly promised Its descent upon the apostles. But tarry ye in the city of Jerusalem, until ye be endued with power from on high (Lk. 24:49), our Lord Jesus Christ commanded His apostles.
Do not ask how the Lord knew beforehand that this power from on high, or the Holy Spirit, would descend upon His disciples…. Even before the Lord spoke of the descent of the Holy Spirit, He already had a zealous and voluntary agreement with the Spirit about this.
More correctly, the Holy Spirit was also speaking through Him about Its descent. For was it not said in the Gospels: Jesus being full of the Holy Ghost (Lk. 4:1)?
And did not our Lord Jesus Christ Himself admit in Nazareth that the prophecy of Isaiah was fulfilled in Him: The Spirit of the Lord is upon me, because he hath anointed me to preach the gospel to the poor (Lk. 4:18)?
Clearly the Son thus abides in ceaseless communion with the Holy Spirit as also with the Father—in a communion of mutual love, obedience and joy. The anointing by the Spirit testifies to the living and true habitation of the Spirit in a specific person.
Then how could the Anointed One say anything about that very Spirit that the Spirit did not already know? Or promise any kind of co-working with that very Spirit if the Spirit had not already agreed to it?
And that the Holy Spirit abided in our Lord Jesus Christ and agreed with His every word, deed, and promise, is witnessed in today’s Gospel reading.
Nikolai Velimirovich (1880-1956; Orthodox Church): The Day of the Holy Trinity. Pentecost: The Gospel of the Descent of the Holy Spirit @ Pravoslavie.