Praying in the spirit is biblical. As Apostle Paul acknowledged:...
Pentecostals, however, have made it into a doctrine that does not square with the Bible. They call it a "Prayer Language" that all Spirit-Baptized belieers should be able to exercise. This goes directly against God's word, as I said.
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"For if I pray in an unknown tongue, my spirit prayeth, but my understanding is unfruitful.
What is it then? I will pray with the spirit, and I will pray with the understanding also: I will sing with the spirit, and I will sing with the understanding also." 1 Corinthians 14:14-15