I Cor 14 > 14-15 For if I pray in a tongue, my spirit prays, but my understanding is unfruitful. 15 What is the conclusion then? I will pray with the spirit, and I will also pray with the understanding. I will sing with the spirit, and I will also sing with the understanding.
II Chro 32 > 24In those days Hezekiah was sick and near death, and he prayed to the Lord; and He spoke to him and gave him a sign.
When we pray in tongues, we pray without understanding. Meaning that we don’t know what we are praying for, but we see the strength and power in that prayer. If we pray in our regular known language, we pray with understanding; meaning we know for what we are praying for. That is why in prayer there are always two sides, a known and an unknown.
The known is called the realm of promise. That means, we claim the promise of God, and we pray by claiming that promise. Many circumstances in our life need a promise of God from the word of God. These promises are claimed through prayer. This is a known realm. This is where we intercede and pour out our supplications to the Lord.