The first amendment to the U.S. Constitution declares,
Congress shall make no law respecting an establishment of religion, or prohibiting the free exercise thereof; or abridging the freedom of speech, or of the press; or the right of the people peaceably to assemble, and to petition the Government for a redress of grievances.
The first restriction on government in the first amendment to the U.S. Constitution prevents the federal government from meddling in religious activity. More specifically, the U.S. Congress is prevented from restricting “the free exercise” of religion.
Simply put, Christians can (must!) be active in government; government is not to interfere with churches or church activities!