Why Christians must pray in tongues?

The Bible talks about the Baptism of the Holy Spirit and praying in tongues in a great length and details. Praying in tongues is not an isolated or outdated practice of the Christian faith, it was one of the main practices of the first century Church. the Lord Jesus Himself said "You will speak in new (unknown) tongue." Mark 16:16-17. Praying in tongues is not praying in any known language but rather it's the main evidence of being baptized with the Holy Spirit. John the Baptist said of the Lord Jesus that He is the baptizer with the Holy Spirit and fire. Mathew 3:11. In Acts 1:4-8 the Lord Jesus spoke of being baptized with the Holy Spirit in order to be an effective witness for the Lord Jesus. Also in Acts 21-5 8:14-18, 9, 10:44-46, 19:1-10 we see that the main concern of the Apostles was to make sure the new believers were baptized with the Holy Spirit with the evidence of praying in tongues. Praying in Tongues has many benefits that we are going to mention a few of them today. 1 cOrinthians 14:2,4,14,15,18 talks in details about praying in tongues, please note that speaking in tongues is different than the gift of praying in tongues. Many people mistaken the two, Praying in tongues is available for all believers but speaking in tongues is only for those to whom the Holy Spirit gives to convey a message to the Church whereas praying in tongues is to pray to God according to His perfect will and it's beyond the constrain of mind.