Man is body, soul and spirit. 1 Thess5:23
The body is a carnal/biological machine that houses the soul and spirit.
“Jesus answered him, “If anyone loves me, he will keep my word, and my Father will love him, and we will come to him and make our home with him.”
It can also house other spirits in some cases hundreds of other spirits.
“Then it says, ‘I will return to my house from which I came.’ And when it comes, it finds the house empty, swept, and put in order.”
The soul of man is understood to be his emotions, will and mind. All immaterial but they act on the body and the body acts on the soul. This would require many verses about I’ll post three one for each
- mind “for wisdom will come into your heart, and knowledge will be pleasant to your soul;”
- will “My soul refuses to touch them; They are as loathsome food to me.”
- emotion “As a deer pants for flowing streams, so pants my soul for you, O God.”
The spirit cannot act on the body without going through the soulish part of man. There is one exception
Speaking in tongues
The spirit of man communicates with the Spirit of God perfectly bypassing the mind of man such that he cannot understand what is being said and the mouth speaks
“For one who speaks in a tongue speaks not to men but to God; for no one understands him, but he utters mysteries in the Spirit.”
1 Corinthians 14:2
In fact this is reiterated by Paul explaining either praying by engaging the mind (soulish part of man) OR praying just with the spirit. He does not speak against either but rather encourages both.
“For if I pray in a tongue, my spirit prays but my mind is unfruitful. What am I to do? I will pray with my spirit, but I will pray with my mind also; I will sing praise with my spirit, but I will sing with my mind also.”
1 Corinthians 14:14-15
To your question why is the person speaking in tongues edifying himself? Or how Is he edifying himself?
“The Spirit himself bears witness with our spirit that we are children of God,”
There is perfect communication unhindered communication between the born again spirit of man and the Spirit of God. Therefore it is a perfect prayer. Such a prayer is the ultimate prayer for oneself because it is not impeded, overridden or hindered by rationalization of the will/emotion/mind of man.
In such a prayer you are praying a perfect prayer according to God’s will. And agreeing with God means getting the highest chance of answered prayers. Answers to prayers are extremely edifying
“And this is the confidence that we have toward him, that if we ask anything according to his will he hears us.”
1 John 5:14
Because joy ought to be complete/full
“Until now you have asked nothing in my name. Ask, and you will receive, that your joy may be full.”