Subsequent to our salvation, God wants to continue to do an empowering work in our lives through the Holy Spirit.

Acts 2:4 NIV
All of them were filled with the Holy Spirit and began to speak in other tongues as the Spirit enabled them.

1 Corinthians 14:1-2 NIV

1 Follow the way of love and eagerly desire gifts of the Spirit, especially prophecy. 2 For anyone who speaks in a tongue does not speak to people but to God. Indeed, no one understands them; they utter mysteries by the Spirit.

"Anyone who speaks in a tongue edifies themselves..." (v.4)
" For if I pray in a tongue, my spirit prays, but my mind is unfruitful." (v.14)

Being filled with the Holy Spirit enables a person to speak in a spiritual language as a way to be spiritually strengthened by communing directly with God in prayer.

1 Corinthians 14:3-4 NIV

3 But the one who prophesies speaks to people for their strengthening, encouraging and comfort. 4 Anyone who speaks in a tongue edifies themselves, but the one who prophesies edifies the church.

1 Corinthians 14:5,13 NIV

5 I would like every one of you to speak in tongues, but I would rather have you prophesy. The one who prophesies is greater than the one who speaks in tongues, unless someone interprets, so that the church may be edified. 
13 For this reason the one who speaks in a tongue should pray that they may interpret what they say.

1 Corinthians 14:16-17 NIV

16 Otherwise when you are praising God in the Spirit, how can someone else, who is now put in the position of an inquirer, say “Amen” to your thanksgiving, since they do not know what you are saying? 17 You are giving thanks well enough, but no one else is edified.

In corporate worship, spiritual gifts are motivated by love and their goal is to strengthen the church.

For verbal gifts to strengthen the church, they must be understood, and function in an orderly manner.

James 3:7-8 NIV
All kinds of animals, birds, reptiles and sea creatures are being tamed and have been tamed by mankind, but no human being can tame the tongue. It is a restless evil, full of deadly poison.