Speaking in Tongues

 "The wind bloweth where it listeth, and thou hearest the sound thereof, but canst not tell whence it cometh, and whither it goeth: so is every one that is born of the Spirit." - John 3:8 KJV

Jesus is explaining that just as the wind has a sound that accompanies it, so likewise the Spirit has a sound that accompanies it. We learn later in Acts, that speaking in tongues is the sound that accompanies the Holy Ghost as Jesus fills an individual with His Spirit.

Acts 2:4 And they were all filled with the Holy Ghost, and began to speak with other tongues, as the Spirit gave them utterance. 

Act 10:45-46 And they of the circumcision which believed were astonished, as many as came with Peter, because that on the Gentiles also was poured out the gift of the Holy Ghost. For they heard them speak with tongues, and magnify God. 

Acts 19:6 And when Paul had laid his hands upon them, the Holy Ghost came on them; and they spake with tongues, and prophesied.

We see from our human experience, that when a baby is born there is a sound. It is when the baby inhales his first breath that the sound is emitted – a cry! This is how we know the baby is alive outside the womb. He must take a breath, or he will die. 

That breath that a baby receives when he is born in the natural is like the Spirit we receive when we are born again of the Spirit. 

Speaking to Nicodemus, 

"Jesus answered and said unto him, Verily, verily, I say unto thee, Except a man be born again, he cannot see the kingdom of God." - John 3:3 KJV

And then,

"Jesus answered, Verily, verily, I say unto thee, Except a man be born of water and of the Spirit, he cannot enter into the kingdom of God." - John 3:5 KJV

So it is as Jesus said, when we are born of the Spirit there is a sound. 

We see in the Bible and from our experience today that this sound is speaking in tongues. 

[Note: Tongues is a language. Tongues as the sign of receiving the Holy Ghost is speaking in a language we do not know, as the Spirit of God speaks through us. We speak in other tongues as God is filling us with His Spirit, trusting and allowing Him to change our words of praise into a language we do not know.]