The Bible strictly forbids syncretistic worship, the mingling of biblical and pagan religions, a violation of the First Commandment.
Praying together is not necessarily an act of syncretism.
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I'm not as pessimistic as the author. I believe that this chastisement has awakened America's sleeping moral sensibility. But I agree that we have a lot of reforming to do, especially regarding the abortion holocaust.
Oh ye it is..They worship false gods..
2 Corinthians 6:14 Be ye not unequally yoked together with unbelievers: for what fellowship hath righteousness with unrighteousness? and what communion hath light with darkness?