Secular Government

A secular government doesn't mean its a form of government that seeks to favor atheism upon free people. That country was called the Soviet Union.  It is critical to insure our freedom that our Government recognizes that only God gives men and women rights in which Government has no authority to redeem (unalienable rights). Once that concept collapses, then the State becomes God and can write changes or limit those freedoms. The State is then the giver, and taker, and not God.
A free people cannot exist without morality, or one willing to submit to the rule of law. The more immoral the population, the more laws and enforcement are required which gradually erodes these freedoms. The inner cities are so immoral (e.g. corruption, crime, and vice), it almost calls for Martial Law (or the suspension of Constitutional rights) to right the ship. A moral population is important to remain free.

The 1st Amendment was written to insure that no man is forced on his knees or forced off his knees. In matters of religion, the Congress has no authority or power. That prohibition applies to creating laws to favor or oppose religion. In no way does that imply individuals in that government cannot openly practice faith as free citizens.

On the other hand, local laws or ordinances that force Christian bakers, florists, or photographers to participate in ceremonies they dim forbidden in their faith practice violates the 1st Amendment rights of their citizens. It favors one religious point of view over another. This is not the "secular" government the founders had in mind.