"We experience sin and alienation from God; the goods are the peace and friendship with God which are the concern of all true religion."
 "Religion is a great blessing, for nothing in life is more important than liberation from sin and friendship with God. However, harmony with God should not be confused with God himself nor with the divine life in which Christians share by adoption. The human good of religion—that harmony with God which perfects human persons as human—is only one human good alongside others (see GS 11). St. Thomas Aquinas makes this point by distinguishing the virtue of religion from the theological virtues. The former, concerned with specifically religious acts, such as prayer and sacrifice, does not bear upon God himself as the latter do (cf. S.t., 2–2, q. 81, a. 5)."
 Finally, in his summary of the seven basic categories of human goods Grisez writes:
"(4) religion or holiness, which is harmony with God, found in the agreement of human individual and communal free choices with God’s will."
Friendship with God is charity, and should not be confused with the virtue of religion. It is not clear to me that Grisez does not muddle the two in , as he says that peace and friendshipw ith God are the concern of all true religion. In  the differentiation is clearer.
In his discussion of religion and its act, devotion, Aquinas seems to be saying that there cannot be the virtue of religion without charity, since religion is concerned with the means to the end which is the object of charity, God Himself. In the response to the first objection, he says:
The power or virtue whose action deals with an end, moves by its command the power or virtue whose action deals with matters directed to that end. Now the theological virtues, faith, hope and charity have an act in reference to God as their proper object: wherefore, by their command, they cause the act of religion, which performs certain deeds directed to God: and so Augustine says that God is worshiped by faith, hope and charity.
Can one will something to God as an end without first loving Him? Can there be the act of religion without the virtue of charity? It seems not: charity is the proximate cause of devotion [religion]. How can someone will something as a means to an end without his will first being referred to the end? Without willing the end, how can the means be a means?
Is religion, then an infused virtue, and not an acquired one? It is apparent that there must be an infused virtue of religion that corresponds to the theological virtue of charity.** But is there a natural, acquired virtue of religion matching the natural love of God? Here we enter into the thicket of controversy: the relationship between the natural order and the supernatural order and the consequences of the Fall and effects of original sin.
I tend to think that there is not an acquired virtue of religion after people attain the use of reason. Either they accept God's grace or they do not.
Germain is clearly doing moral theology in his books. But if he follows Aquinas (or this understanding of Aquinas) and implicitly admits in his account of natural law that religion is thus tied to charity, then its usefulness ends. What is needed for non-believers beyond this point, as I said earlier, is not more discourse about the precepts of the natural law, but grace and Christ.
I should compare this with what Finnis writes about the good of religion...
I note that a special issue of the American Journal of Jurisprudence was devoted to Grisez on the question of human fulfillment, and iirc, some of the contributions examined his treatment of religion.
On religion as "belief system" or "worldview":
In a comment to a previous post from today JBS gives a definition of religion:
Religion - that set of rules by which I know I'm ok...and you're not.
This definition allows for many belief-systems not normally thought-of as 'religious' to function, allowing for everyone to have a religion, apart from a real relationship with God.
It seems that here religion is synonymous with belief system or world view. Everyone has a belief system or worldview, which is a mixture of knowledge and set of beliefs about reality. But it is not the same as religion as it is defined by Grisez or Aquinas. People act in accordance with certain first principles, but these first principles may not include God.
What about the pagans and their beliefs and attitudes? Is God or are the gods superior to us? Hence we must give them the proper respect and may even need to placate their anger. Or are they merely used by us? That is, they are servants of our happiness. Whom must we please? Ourselves or the gods?
If the virtue of religion is tied to the love of God, then what motivates those who do not love God but are "imperfect" to perform certain acts of religion? The fear of punishment or the promise of reward (or a certain good of reason), which can be harmonized with the love of self. One does not need the love of God to fear punishment, etc. Similarly, non-Christians do not need charity in order to perform the rituals that they have learned from their elders. Just because certain acts associated with a virtue are being done does not imply that this virtue is present in the agent.
We can use Aquinas's treatment of the Old Law as a model for understanding non-Christian religions*** before the coming of Christ and relate their proximity to the truth through the supposition of a Primitive Revelation. See Journet's The Meaning of Grace for his account of grace before the Incarnation and "God in Search of Man" by Patrick Beeman for more about Wilhelm Schmidt.