Today is National Day of Prayer. This holiday is a mistake. There are ways it could be celebrated that I would potentially support. There are Biblical approaches to this holiday which would at least prevent it from being outright idolatry, but the way that the holiday actually is observed is not something I can support at all.
First the reasons why you should not observe this holiday:
1. It is an infringement on secularism. We are a secular republic and the state should not be in the business of lifting up any particular religion over another. Though the holiday is vague enough it could apply to a variety of faiths, in practice it is dominated by Christians. Last year every other prayer at the event held in City Park in my town included something about this being a "Christian Nation." Increasingly, secularism is also understood to mean not lifting up religiousness over a-religiousness. Even if the holiday were perfectly pluralist it would still be infringing on atheists who are part of our nation.
2. As it is usually practiced it is idolatrous. It is possible to pray "for the nation" in a way that is not idolatrous, but to lavish praise, swear an oath of allegiance, kiss or salute or otherwise honor symbols of patriotism and national pride like the flag, or refer to the United States or any nation as somehow uniquely important to God, belonging to God or held in special esteem by God is idolatry. God is not American. In fact, God is steadfastly against national identity, ethnic divisions, divisions of class, and gender. God is busily working to unite all people and the powers and principalities are God's implacable opponents in this world. It is doubtful that any kind of prayer, but a prayer of repentance is appropriate for a nation state.
3. The kinds of prayers which would be appropriate on a "National Day of Prayer" from a Christian perspective, are necessary all the time. Prayers of repentance. Prayers for justice. Prayers for peace. Prayers for the end of nations and the inauguration of the kingdom. We should be praying like that all the time, and we should definitely not be praying on a schedule dictated by congress and signed into law by the president. If anything we should be calling for Christians nationwide to hold prayer vigils around the anniversary of wars and actions that our country needs forgiveness for. We should call for non-participation of Christians in holidays like this one which serve to buoy national pride and entrench parochialism. National Day of Prayer, Memorial Day, Independence Day, Veterans Day, President's Day... these are days for us to boycott, not observe.
Now an approach to the holiday which would win my tepid support (not overcoming all my objections, but a start):
1. National Day of Prayer as a day of atonement. If we assembled prepared for mourning and repentance, dressed in sackcloth as it were, and did so in open areas devoid of any symbol of national pride or identity; if at such an assembly we said aloud and forcefully our many sins - the wars we have waged and are waging, the injustices of our economic system, the division of classes and racial and gender inequalities in our society, the fearful grasping after security, and failure to trust God's providence, the perpetuation of our identity over against imaginary "enemies" and the hatred of those enemies we have created - THEN we would be on the right path.
2. Following our rehearsal of our sins, we would hear from the prophets of the Old Testament warning the nation of Israel that God held them in no special regard, but would judge them for failing to be a light in the world. We would remind ourselves that God in Jesus calls the entire world to communion and we have no business coming to that table as Americans, or Brits, or Chinese, or Russians.
3. Finally, we would pray that God would forgive the sins of the whole world, end divisions and inaugurate an era of Shalom. We would repent of any national allegiance and vow never to take up arms against a neighbor so that we might have a place in that new world. Then we would go home weeping, knowing that it was too little too late.