From The Trinitarian Faith
When the Holy Spirit is given to us, God is in us, and if the homoousion holds true, then Christ is in us. “It is not merely by his power or operation, but God himself is present to us in his being.
Didymus rebuts Basil’s distinction between the energies/operations of God and the immediate activity of his being…for it would damage a proper understanding of the real presence of God to us in his Spirit” (Torrance 210).
Cf. Didymus, De Spiritu St 23ff, 60ff. De Trin could speak of the indwelling presence of the Holy Spirit as the presence of God secundum substantium and not merely secundum operationem.
Also see Theology in Reconstruction, 210-213.