(4) There can be no real equality between God and the human soul, but God in His infinite goodness, elevating the soul to a higher plane and allowing it to participate in His own nature,(1085) makes possible an _amicitia excellentiae s. eminentiae_, which is sufficient to constitute a true relation of friendship. Without this elevation of the soul by grace there could be no friendship between God and man.(1086)
4. ADOPTIVE SONSHIP.—The formal effects of sanctifying grace culminate in the elevation of man to the rank of an adopted child of God (_filius Dei adoptivus_), with a claim to the paternal inheritance, _i.e._ the beatific vision in Heaven. This truth is so clearly stated in Scripture and Tradition that its denial would be heretical. The Tridentine Council summarily describes justification as “the state of grace and of the adoption of the sons of God,”(1087) The teaching of Holy Scripture can be gathered from such texts as the following. Rom. VIII, 15 sqq.: “... You have received the spirit of adoption of sons, whereby we cry: Abba (Father). For the spirit himself giveth testimony to our spirit, that we are the sons of God. And if sons, heirs also; heirs indeed of God, and joint heirs with Christ.”(1088) 1 John III, 1 sq.: “Behold what manner of charity the Father hath bestowed upon us, that we should be called, and should be the sons of God.... Dearly beloved, we are now the sons of God.”(1089) Gal. IV, 5: “... that we might receive the adoption of sons.”(1090) That the just become the adopted sons of God follows likewise as a corollary from the doctrine of regeneration so frequently taught by Scripture. This regeneration is not a procession of the soul from the divine essence, but a kind of accidental and analogical procreation substantially identical with adoption (_filiatio adoptiva_, υἱοθεσία). Cfr. John I, 12 sq.: “... He gave them power to be made the sons of God, ... who are born ... of God.”(1091)
a) St. Thomas defines adoption as “the gratuitous acceptance of a child of other parents to be the same as one’s own child and heir.”(1092) Adoption implies (1) that the adopted child be a stranger to the adopting father; (2) that it have no legal claim to adoption; (3) that it give its consent to being adopted; (4) that it be received by the adopting father with parental love and affection. All these elements are present, in a far higher and more perfect form, in the adoption of a soul by God.