The biggest miracle for me when it comes to praying in tongues is the ability to understand God and start comprehending His ways.
This was not true in the Old Testament and only a few stood out. There were prophecies many prophets gave in the Old Testament that the people do not understand. The understanding of the people was very dull in that dispensation to the extent that when God gave instructions, they simply lack the desire to follow them.
At certain times, in a bid to solve the hearing and seeing problem; God would tell the Prophets to physically act out His instructions so that the Israelites could understand. They were dull of hearing; their understanding was not quickened and they could not perceive even when they see. They still fall victim to the very thing God warned them about.
After the fall, Cain was the first person to show this trait. God clearly told him sin desired to have him and he should rule over it but Cain did otherwise. He could simply not understand or perceive, therefore, he lacked the inspiration to act accordingly.
Despite the acts of God amidst the Israelites, they could not understand Him. He started showing them a new culture — to reorient their minds yet they will fight it. Only one-man Moses could understand God and a few others (Joshua and Caleb…).
When Jesus came, He declared Himself as the perfect image and expression of the Father so at least they could understand God the way they were supposed to, the Pharisees, Sadducees and their followers were still dull of hearing and they could not perceive. To a large extent, the disciples because they believed in Jesus, could understand some things but they were in limbo on many other teachings of Christ.
This problem changed when Jesus died and was resurrected which paved the way for us to receive the Holy Spirit — the enablement and the power from the Father. It is called a quickening Spirit in Romans 8:11. The Holy Spirit will not just quicken your spirit and body, He will quicken your mind too. He quickens every part of you — conscience, mind, will, intellect, body, spirit, emotion, sub-conscience… every part of you.
Praying in tongues is a means to an end not an end in itself. The perfect way to pray is to pray in tongues. When we pray in tongues, there is a flow of power from the Holy Spirit, it operates like energy and starts flowing through your systems, suddenly you can comprehend scriptures, Jesus called it understanding when you hear and perception when you see. If you do not understand after hearing you have not heard and if you do not perceive after seeing you have not seen. The problem is the heart; the heart is dull. The power of the Holy Spirit does a corrective surgery whenever you are praying in tongues. At this point, you start understanding God and His ways. The more you pray, read the word and fellowship with the Holy Spirit, the knowledge of God grows in you.
One of the testimonies I received this week, and it gladdens my heart is the video attached to this Tweet. When you pray in the Holy Ghost, you become aware of the desires of the Father so it is easy to make declarations in understanding. Prayer becomes an enjoyable activity for you and you will always want to pray.
Yes, I believe the ability to comprehend God and walk in His ways is a miracle.