I know I'm late in coming to this observation. I do not doubt that if you were to make a cursory search of the great saints and theologians of Church history, it would not be difficult to find dozens who long ago arrived at what I am about to write about. However, I will give thanks that at least this little bit of light was given to me; no doubt, its seed was planted by something I read or heard over the years, so if someone recognizes this as something he or she told me long ago, please accept my thanks and let me know of that so I may give proper acknowledgment.
Over the past couple of days it has slowly dawned on me that there is something in the nature of love that is obligatory. Not that one is obliged to love, for that would contradict its very nature as an act freely chosen and freely given.
No, love is willing to make itself obligated to the beloved. If I do not have love for someone or something, then I have no obligation to help that person or thing. For instance (and this is a silly example, but let's start out small), if I have no love for a mouse and I see one stuck in a trap, I can walk by that mouse or even pick it up and throw it out. However, if I have a love for mice, even if that is simply affection, then I will do what I can to save it. My freely chosen love for the mouse has put me in the place where I am obliged to help it out.
The same goes for love of persons. Falling in love is something of a misnomer for it implies that I am impelled to love this one particular person, which is not true. It is also implies that I can fall out of love as well. However, it is in the nature of love to give of oneself to the other and that giving necessarily obligates oneself to do something for the good of the other. If I have no love for people and I see someone in need, I am not under an obligation to help that person out. There may be some exterior compulsion to do that, but it is not an interior obligation caused by love.
On the other hand, if I choose to love someone in whatever way that person is to be loved (philia, eros, agape), then I am now under an obligation to help that person who is in need. That help may be shown in a variety of ways, including so-called 'tough love.' But the obligation remains no matter how varied the help given might be.
If I marry, then I place upon myself the obligation to care for this person's welfare. In fact, love makes it obligatory that I place the needs of my beloved above my own. Love should be glad to do what is necessary for the beloved, even when what is necessary is irritating, not what I want to do at the moment, not what I think is important, or requires true sacrifice on my part.
God was under no obligation to make us. However, once He did so, He put Himself under the obligation of love to help us out of our self-imposed dilemma. His ultimate sacrifice on the Cross is the sign par exellence of what the obligations of love will do.