“to have given His Son unless he were to give the Holy Spirit also ….”
“How ineffable is God, how unutterable his mercy. Wonderful his name, wonderful all his works. Truly the esteem in which the divine love holds us is completely inexpressible. It was not enough for the Father to have given his son to redeem his slave, unless he were to give the Holy Spirit also, through whom he adopts the slave as his son. He gave his Son as the price of redemption; he gave the Spirit as the bill of adoption. Finally, he reserves himself in all his totality as the inheritance of those he has adopted.
O God, if I may be allowed to speak thus, you lavish yourself on man far beyond his dreams. Is he not lavish who brings to bear not only all his resources but even his own person in order to win back mankind, and this not for his own sake but for the sake man himself? Is he not lavish? Just as he did not spare his own Son but gave him up for us all, so also he has, so to speak, not spared the Holy Spirit, but has poured him out on all flesh with a liberality of a new and astonishing depth.
Prodigal indeed was that Son who lavished both his inheritance and himself on harlots. His Father however was much more prodigal in winning back his lost son than the son had been in brining about his own ruin; if there can be any real comparison between grace and money, spirit and flesh, God and man.”
— Guerric of Igny, Sermon 38 —