Yet they are told they must embrace the Christian Faith immediately, without hearing any sermon preached...They are told to subject themselves to a King they have never heard of nor seen...
So writes Bartolomé De Las Casas in his The Devastation of the Indies about many unjustified attacks upon natives who were given the option to submit to the Crown of Spain with very little time before being attacked. [Herma Briffault tr., Johns Hopkins University Press: 1992, p.49] Behind this objection to one of the many inhumanities of some of the conquistadors is a very good question: "How can we love God if we've never seen or met Him?" "Can we truly love Him?"
True, people can honor their ancestors even if they never knew them. When Joan of Arc lifted the Siege of Orléans, the people venerated three French saints from 1000 years earlier much more than the actual person who rallied the troops. But obviously there's a difference between a personal connection of a long-gone ancestor and something like your parents or siblings whom you've experienced on a daily basis.
But the answer is pretty simple in my opinion. Let's take the example of patriotism. Patriotism is love of country. Obviously the country means the people, so it's love of the people. Yet if we take the U.S. with its 300+ million people, reduce that to something like ~100 million ages 30 and over, assuming you met a different person who became a close friend and with whom you spent enough time every month, a 30 year old person could've hardly met and known much more than about ~400 people this way. This means a person would've met only about 0.00004% of the population. Nobody has like 400 close friends. The average person wouldn't even have 40 (0.000004%). So, what - someone can't be a patriot for the entire country? Only for the neighborhood of his town? Clearly not. And just as there are different kinds of love and connections, in the same way God could easily have created man so that he can be in communion with Him without having to physically be present.
In the end, a physical presence can produce bias, and with a (temporary!) absence of it, the righteous person should still function with holiness.