It refers to the fact that the Founding Fathers of the USA were anxious to unite their colonies and its different citizens into one united people, not on the basis of race or geography, but on the basis of a shared approach to liberty under law in a republican form of government (a "republic" is a representative form of government in which government is "of the people, by the people and for the people," as Abraham Lincoln described it.
Now this motto, E Pluribus Unum, envisions a geographically diverse people of farmers, businessmen, laborers, etc., working together voluntarily in a nation where every member of society is free to pursue his own happiness under laws that are passed for the good of all. Laws such as stopping as stop signs and driving on the right side of the road make what would otherwise be extremely dangerous actions, such as passing a car going 60 mph the other way only four feet away, very safe.
This principle is also expressed in our Pledge of Allegiance to the American flag in the words, "one nation under God, indivisible, with liberty and justice for all." A people committed to the same laws applying to all citizens lives in peace and tranquility and is truly "indivisible." But drop God as the source of moral law out of the equation, and law becomes just another man's opinion, easily broken without consequences.
E Pluribus Unum, however, speaks to another aspect of community life that is just as important as living under laws written in lawbooks, and that is of doing good in positive ways. Lawbook, or "case" laws, are written to set up punishments for folks who do bad things; they say nothing about people who do good things.
For example, there is no law rewarding the person who returns a found item to its rightful owner as everyone should, or to reward neighbors who harvest a crop for a fellow farmer who is stricken with some illness. We all ought to do these things simply because they are good things to do, they are a part of being "one nation under God," and they carry out E Pluribus Unum.
It seems to me that it is in this context that we ought to deal with the energy crisis in America. We could easily reduce our use of gasoline and fuel oil considerably by doing what is good for the rest of society as well as for ourselves, namely using as little fuel as is necessary for any task or trip. The thing is that we are in this fuel shortage together.
Every gallon of gas I use cannot be used by anyone else; it is gone for good. So when I use my 13 mpg 3/4 ton van to carry my little body (less than 200 pounds) and nothing else, I am less than as good a citizen as I could be by using my car that gets better than twice that mileage. On the other hand, there is nothing wrong with using the van when the load makes it necessary.
We could use a little more E Pluribus Unum in our nation today, especially seeing that it is printed on all our coins. When I think I should be able to burn as much gas as I can afford, I am forgetting my neighbor, whom God commands me to love.