There is a strong tendency for people to read things with which they agree. Thus, there is an element of preaching to the converted in every column, and that is truer of what you are about to read than is usual: It is an argument that people should vote, being made to people who are already very likely to cast ballots.

But I am writing it anyway for two reasons.

First, preaching to the converted is an entirely honorable activity: If it were prohibited, unemployment would rise, as most members of the clergy would find themselves out of work.

Second, speaking to those who are like-minded can give them arguments to use in spreading the word. I hope that those who already understand how important it is to cast their ballots will find some of this useful in persuading those who might not otherwise do so to follow their example.

The most blatant efforts to keep people from voting have come from conservatives, who have outrageously used their control of state governments to adopt laws and regulations making it more difficult for people to vote by requiring the production of a variety of documents that many older and lower-income people will have difficulty providing.

But my concern today is with my friends on the left who discourage others from voting by their rhetoric.

n First, there is the wholly inaccurate assertion that there are no real differences between the two political parties. In fact, the differences between the Democratic and Republican parties today are sharper than they have been since the Civil War.

At the federal level, if the Democrats retain the U.S. Senate, and a Supreme Court vacancy occurs, the president will be able to nominate a successor who will probably be confirmed. This will not happen if the Republicans take control. Those who support the Citizens United decision, which said that corporations may spend freely in political campaigns, will get their way if the Republicans win; those of us who wish to change it will benefit from a Democratic victory.

Similarly, efforts by the Obama administration to deal with climate change will be retarded, if not thwarted, if the Republicans control both houses of Congress, while continued Democratic control of the Senate will mean that the Environmental Protection Agency can go forward on this issue.

In an area very close to my interest, Sen. Mitch McConnell of Kentucky has announced that if he becomes majority leader, Republicans will use the appropriations process to cut back on the financial reform bill, including severe restrictions on the independence of the Consumer Financial Protection Bureau, and a re-deregulation of derivatives.

Here in Maine, there are very clear differences that will result depending on the election for governor. As independent candidate Eliot Cutler implicitly acknowledged last Wednesday, the governor in January will be either Democratic U.S. Rep. Mike Michaud or Republican Gov. Paul LePage.

If it is LePage, there will be no increase in the minimum wage in the state and no adoption of the expansion of Medicaid that is included in the Affordable Care Act, with the federal government paying almost all of the cost. If Michaud wins, the minimum wage very likely will be raised and Medicaid extended.

At both the federal and state levels, there are a variety of other differences as well. In fact, many of those who are most unhappy with the current political system believe that there are too many differences.

I agree that the sharpening of partisan divisions that has occurred over the past 20 years is unhealthy. This situation calls for two responses: working to reduce the differences over time, and taking account of the ones that exist in any given election. People who want to restrict campaign spending, take government action to deal with climate change, raise the minimum wage and extend health care should vote Democratic. Those who oppose these goals should vote Republican.

n The second argument that the left uses against voting is that even while there might be sharp differences in the two parties’ platforms, once people are elected, they ignore the wishes of the constituents and listen only to the big contributors.

I very much agree that big money has too much influence in our politics. But the argument that money dominates everything and that politicians pay no attention to voter sentiment is a graphic example of a self-fulfilling prophecy. Tell people that their vote does not matter, and that there is no point in trying to influence elected officials, and many of them will act on that advice.

When our committee approved the independent Consumer Financial Protection Bureau, Democratic Sen. Elizabeth Warren of Massachusetts said to the media, “They told me not even to try this because the banks always win. But they didn’t win today.”

The reason they didn’t is that anger at the financial crisis had energized enough private citizens so that they spoke out. My colleagues knew when we voted on the issue that we were about to make a very public choice between the influence of big contributors and the sentiments of their voters. Voter sentiment won.

As I write this, I do regret that I did not do it earlier. I noted above that the very partisan divisions that seem to be relevant in people’s decisions to cast their votes have gotten too sharp, and I believe that there is a strong argument for trying to reduce them. But that cannot be done unless more people vote in primaries.

As long as it is the self-selected ideologically committed activists who dominate party primaries, while more moderate voters stay home, ideological division will increase. That has become particularly the case in the Republican Party – witness Mitt Romney’s dilemma in 2012. He had to move to his right to win the nomination, and then try to move – awkwardly – more to the center for the general election.

It is hard for people to keep two somewhat distinct ideas in their heads at one time, but that is what the rational voter should be doing today.

Approaching an election in which there are two political parties with sharply different views on virtually every issue, voters who care about these outcomes should vote for the candidates of the party that comes closest to their views. Immediately after voting, they should begin the effort to support those in the party they prefer – and, indeed, in both parties – who are seeking nominations with more moderate positions.

One thing is absolutely certain: The more people who are dissatisfied with the status quo listen to those who tell them not to bother voting, the more entrenched the status quo will become.

Barney Frank is a retired congressman and the author of landmark legislation. He divides his time between Maine and Massachusetts.

Twitter: @BarneyFrank