The Holy Spirit
A person can abide in Christ, accomplish His: commandments and be in communion with God the Father only by the presence and power of the Holy Spirit in his life. Spiritual life is life in and by the Holy Spirit of God.
If you love me (says Christ), you will keep my commandments. And I will pray the Father, and He will give you another Comforter to be with you forever, even the Spirit of Truth, whom the world cannot receive, because it neither sees Him nor knows Him; you know Him, for He dwells with you and will be in you (Jn 14:15-17). When the Spirit of Truth comes, He will guide you into all the truth. ...He will glorify me, for He will take what is mine and declare it to you. All that the Father has is mine… (Jn 16:12-15).
The Holy Spirit proceeds from the Father and is sent into the world through Christ so that human persons an fulfill God’s will in their lives and be like Christ. The spiritual fathers of the Orthodox Church say that he Holy Spirit makes people to be “christs,” that is, the “anointed” children of God. This also is the teaching of the apostles in the New Testament writings:
But you have been anointed by the Holy One and you know all things… and the unction [chrisma] you have received from Him abides in you… His anointing teaches you about everything and is true and is no lie, just as it has taught you, abide in Him. [...] And by this we know that We abides in us, by the Spirit which He has given us. [... ] By this we know that we abide in Him and He in us, because lie has given us of His own Spirit (1 Jn 2:20-27, 3:24, 4:13).
This teaching of Saint John is the same teaching as that of Saint Paul.
... God’s love has been poured into our hearts through the Holy Spirit which has been given to us. [...] Any one who does not have the Spirit of Christ does Christ does not belong to Him. But if Christ is in you, although your bodies are dead because of sin, your spirits are alive because of righteousness. If the Spirit of Him who raised Jesus from the dead dwells in you, tie who raised Christ Jesus from the dead will give life to your mortal bodies also through His Spirit which dwells in you… for if you live according to the flesh you will die, but if by the Spirit you put to death the deeds of the body, you will live. For all who are led by the Spirit of God are sons of God (Rom 5:5, 8:1ff; cf. 1 Cor 2, 6, 12-14; Gal 5).
It is the classical teaching of the Orthodox Church, made popular in recent times by St Seraphim of Sarov (19th c.), that the very essence of Christian spiritual life, the very essence of life itself, is the “acquisition of the Holy Spirit of God.” Without the Holy Spirit, there is no true life for man.
In spite of our sinfulness, in spite of the darkness surrounding our souls, the Grace of the Holy Spirit, conferred by baptism in the name of the Father and the Son and the Holy Spirit, still shines in our hearts with the inextinguishable light of Christ… and when the sinner turns to the way of repentance the light smooths away every trace of the sins committed, clothing the former sinner in the garments of incorruption, spun of the Grace of the Holy Spirit. It is this acquisition of the Holy Spirit about which I have been speaking. ...(St Seraphim of Sarov, Conversation with Motovilov).