"In both these texts [(Gal 4:6 and Rom 8:14-17)], the invocation Abba, which has up till now been a prerogative of Jesus, appears from now on as our own property. What made this transformation possible is not a method of prayer that Jesus revealed to us in secret, but the gift of the Holy Spirit who prays to the Father in us just as he prays in Jesus. Christian prayer is thus much more than the imitation of a model: it is the fruit of a configuration. We do not only pray 'as Jesus'; it is Jesus who prays in us. He prays in us in the Holy Spirit, who is the soul of our prayer. And this action of the Holy Spirit does not dispossess us of any part of ourselves or our freedom, since the Spirit of God 'bears witness to our spirit' that we are his children: he does not take the place of the created spirit, but gives it the capacity at last to realize that for which it was made."
Jean-Pierre Batut, "Praying to the Father through the Son in the Spirit: reflections on the specificity of Christian prayer," trans. Michelle K. Borras, Communio: the international Catholic review 36, no. 4 (Winter 2009): 634-635 (623-642).