Through Christ [God] forgives everything, through the Spirit he charges us with nothing.… And so Christ is in a certain sense the mediator for justice, while the Spirit is the mediator for friendship. Christ mediates for truth, the Spirit for charity; Christ for forgiveness, the Spirit for safeguarding; Christ for mercy, the Spirit for perseverance; Christ for absolution, the Spirit for binding together. Yet both Christ and the Spirit do everything inseparably. For the Father, the Son, and Holy Spirit do everything together and in the same way; they are one without confusion and three without division.
Yet the Son is, in a certain sense, a kind of ambassador from the Father, who alone sent him, and the Spirit is a kind of ambassador from both, for they both sent him. Therefore the Son appeases the angry Father, as it were, and undoes his hostility; the Spirit in a certain sense calms and soothes, as it were, the most just one, and joins us to him in friendship. The Son intercedes as reconciler and advocate between the perpetrators’ wickedness and the Judge’s fairness; the Spirit intervenes as comforter and Paraclete between the weakness of those now reconciled and the majesty of him now appeased.
Isaac of Stella, Sermons on the Christian Year, Volume Two, Sermon 45: Third Sermon for the Day of Pentecost, v. 13, 14, 15 (CF 66, p. 131f)