What is the function of the State of the Union Address? What answer do you give? If you say that it's a constitutional duty, you are missing the point. If you think it's to assess the state of the union, you are missing the point. If you think it's an opportunity for the president to move his legislative agenda, you are missing the point. If you think it's a chance for the president to lead, you are off the mark too.
What then? The function of it is to hold the State together by holding together the masses of Americans that consent to the State and think it a good bargain. This address is a ritual designed to reinforce the aggregation of citizens into the mass that supports the State. When the opposition presents its case, the function is precisely the same. The content of these presentations is peripheral to the ritual itself. The ritual defines a shared political connection. The content is secondary. The content is the "what" that is posited to be done, upon which there is always disagreement, but sharing in the ritual is a commitment to the process and thus the State, no matter what its outcome.
Politicians are continually engaged in supplying the ritualistic glue that holds the body politic together. They continually are plucking the strings of sentiment, interest and morality. Their job is continually to hold together their governments and induce people to think that the governments are acting morally in the interests of society.
Some other institutions also have annual "state" addresses to do the same. Some university presidents do this. Governors do this.
In many speeches and maybe in tonight's speech, the speaker openly intones the ritual of "fellow Americans" or the "coming together" or constantly says "we" face "common problems" and "we must do this or that." The whole idea of this rhetoric is to solidify citizen support of the State, since so many of us actually suffer at its hands. The politicians have to use every opportunity to convince people that their "sacrifice" (really their pain) is worth it or that there is some sort of greater social good that the rulers are engaged in producing, with the cooperation of all those who are suffering under their rule.
The major media are a transmission belt for politicians to reach the people, so that they can accomplish their aim: hold the State together. Cement it as a beneficial institution in people's minds, despite the evident pain it causes and burdens it imposes.
Any threat to the solidity of the State, however slight, however remote, will be greeted by the State with overwhelming rebuttal. If police are attacked, you can be certain that the State's response will be entirely in favor of the police, even if the police are rife with misconduct.
The State exists as something of value in people's minds. The Constitution strengthens that valuation. That is its purpose. It is to institutionalize the State and give it long-lasting continuity.
Look at the State's response to whistleblowers in the CIA, to Assange and to Manning. These are examples of the thesis I am propounding. The State has to hold onto the consent of masses of people, and it cannot allow threats to blossom that threaten to separate and splinter its core support. If speech threatens to do that, I predict that the State will make an attempt to suppress that speech and/or the speakers. It will, in fact, kill its opponents who threaten its existence by getting in between the State's agenda and the masses that it has organized to support it and its agenda. Faced with splintering, secession, rebellion, and mass discontent, all states turn to repression, killing, imprisoning, and attempts to disgrace their opponents.
For a State, its survival is the number one priority. The State of the Union Address is one more tool by which it engages susceptible members of the public and lures them into playing its game on its terms. The goal is to reinforce consent to the State via togetherness and unity in a common process of striving. It is to make people forget the pain, travail, death, taxes and controls imposed by the State.