What is love? That's the question! We are told to love our neighbors as we love ourselves. How are we supposed to do that? Does love mean that I affirm the neighbor in her interests and concerns, whatever they might be, provided that they are personally fulfilling for her? On the other hand, does love mean that I direct my neighbor towards what is objectively fulfilling for all human persons, even if she might not see this at the moment?
Augustine answers this question in a discussion about the impropriety of worship of angels. Is it proper to worship angels? If angels love us, would they require us to worship them? Augustine's answer is straightforward and clear:
We are commanded to love this Good [viz., God] with all our heart, with all our soul, with all our strength; and to this Good we must be led by those who love us, and to it we must lead those whom we love. Thus are fulfilled those commands on which 'all the Law and the prophets depend': 'Thou shalt love the Lord thy God with all thy heart, with all thy soul, and with all thy mind', and, 'Thou shalt love thy neighbor as thyself.' For in order that a man may know how to love himself an end has been established for him to which he is to refer all his action, so that he may attain to bliss. For if a man loves himself, his one wish is to achieve blessedness. Now this end is 'to cling to God.' Thus, if a man knows how to love himself, the commandment to love his neighbor bids him to do all he can to bring his neighbor to love God. This is the worship of God; this is true religion; this is the right kind of devotion; this is the service which is owed to God alone (City of God, X.3).
For Augustine, then, to love the other person ultimately cannot be separated from leading her to love God, because this is the ultimate good for every human person. The good life for a human person has this ultimately objective element, even if it is appropriated differently by persons of different temperaments and capacities and abilities: the good life consists in clinging to God, loving God and living in obedience to his commandments.
If this is what the good life is, then I am not doing my neighbor any favors when I encourage her to do things which are incompatible with this! At the same time, if I fail to provide any kind of testimony to my neighbor that a life with God is worth living -- for example, if I do not trust in God in difficult times; if I don't obey his commandments even they are difficult; if I don't tell other people about God at all -- then I am doing a double disservice: I deceive myself in thinking that I actually live a life with God, and I provide a poor testimony to the Christian religion to my neighbor who doesn't believe.