It is one of the gifts of the holyspirit that helps us to be edified or built spiritually and increasing our faith. Jude 1:20 says we should build ourselves up on our most holy faith by praying in the holyghost. It helps us to speak directly to God amidst obstacles put by the devil against our prayers. Ephesians 6:12 says we wrestle against powers and pricipalities, against spiritual wickedness in the heavenly places. It helps us to pray for the un known. John 4:4 says those who worship God must worship him in spirit and in truth. We do not know how we ought to pray but the spirit makes intercessions for us with groanings that can not be uttered.( Romans 8:26). We speak mysteries to God. Not even the devil understands what we speak to God.