17. I have dwelt upon these facts because the heretics falsely maintain that the union between Father and Son is one of will only, and make use of the example of our own union with God, as though we were united to the Son and through the Son to the Father by mere obedience and a devout will, and none of the natural verity of communion were vouchsafed us through the sacrament of the Body and Blood; although the glory of the Son bestowed upon us through the Son abiding in us after the flesh, while we are united in Him corporeally and inseparably, bids us preach the mystery of the true and natural unity.