On Monday the United States will celebrate one of its great festivals of civil religion as Barack Obama is inaugurated for a second time. Although nothing in the Constitution mandates it (the only things the Constitution specifies are the date and the wording of the oath), the ceremony will include an invocation, a benediction, undoubtedly one or more mentions of God in the inaugural address, and the words “so help me God” as part of the oath of office. These words are often attributed to George Washington (he allegedly added them to his oath in 1789, but no extant contemporary evidence proves that he did). The historical record indicates instead that these words were probably first spoken in 1881 by Chester Arthur when he was sworn in following James Garfield’s death. Of the nation’s 56 inaugural addresses, only Washington’s very brief second one (135 words) does not refer to God. All others have invoked His presence, asked for His blessings, and/or celebrated His relationship with the United States.

In addition, on Tuesday morning President Obama and Vice President Joe Biden, along with numerous dignitaries and Americans of varied faiths, will attend a worship service at the Washington National Cathedral, which will include prayers, scriptural readings, and musical performances. The event is not open to the public, but it will be webcast live.

Why do the inauguration festivities include so many religious components? The basic answer is because of our civil religious traditions and the expectations of Americans. Throughout American history our national magistrates, whatever their private religious beliefs, have been guided by America’s civil religion in performing their official duties. Presidents have extensively employed religious rhetoric in various settings for numerous reasons: to express their deepest convictions, help accomplish their purposes, unite and inspire citizens, provide comfort and consolation, stimulate people to take certain actions, justify the nation’s exploits, and hold citizens and the country accountable to transcendent standards.

Regularly invoking God in inaugural addresses and on other important occasions, the president has functioned as the nation’s “principal prophet, high priest, first preacher, and chief pastor.” Presidents have used religious rhetoric to reassure citizens that God rules the universe and loves them as Americans fought enemies in various wars and coped with disasters in space and terrorist threats and mass murders at home. They have also used biblical images and metaphors because they resonate with many citizens and have tremendous evocative power.

“The knowledge that God calls on us to shape an uncertain destiny,” Barack Obama proclaimed in his first inaugural address, “is the source of our confidence.” Obama also accentuated God’s grace and asked Him to bless the United States. In both campaigning for office and as president, Obama has testified to his personal faith. While he strives to represent and serve all Americans – “Christians and Muslims, Jews and Hindus, and non-believers” – as he put in his first inaugural address, he has frequently confessed his “faith in Jesus Christ as his savior and Lord.” He used religious language and scriptural quotations to comfort families who lost members at Aurora and Newtown.

Presidents have sometimes employed the argument that the United States is God’s chosen nation or has a divine mission to justify military intervention, diplomatic coercion, and cultural imperialism in ways that have violated the self-determination of nations. Sadly, such claims have displayed American arrogance, ethnocentrism, and provincialism. Religious rhetoric has also been used to reinforce the assumption that American moral values and political principles are superior to those of other nations.

However, for the most part, whether it has been employed in a priestly way to console or a prophetic way to challenge, presidents’ use of religious rhetoric has often been beneficial. In the absence of a national church or an official religion, civil religion has served as a glue to help hold Americans of diverse backgrounds, ethnicities, and ideologies together and to motivate them to work to achieve widely shared goals. It has also served as powerful foundation for moral order.

Religion of all types, especially Christianity, which has been America’s predominant faith, has promoted and inspired upright moral conduct. Religion fosters “generosity, law-abidingness, helpfulness to others, civic engagement, social trust,” and other traits that are essential to the flourishing of a republic. Moreover, history demonstrates that most people have a strong need to find a deeper purpose in life than mundane, daily activities supply. “Civil religion,” historian Wilfred McClay, argues, “serves this need … by linking the ongoing life of the nation to a community of memory, and to transcendent moral and spiritual order.” By so doing, civil religion helps “hold the state accountable to a standard higher than itself.”

Dr. Gary Scott Smith chairs the history department at Grove City College and is a fellow for faith and the presidency with The Center for Vision & Values. He is the author of “Faith and the Presidency From George Washington to George W. Bush” (Oxford University Press, 2009) and “Heaven in the American Imagination” (Oxford University Press, 2011).