1st Corinthians 14:15

12 so also ye, since ye are earnestly desirous of spiritual gifts, for the building up of the assembly seek that ye may abound;

13 wherefore he who is speaking in an [unknown] tongue -- let him pray that he may interpret;

14 for if I pray in an [unknown] tongue, my spirit doth pray, and my understanding is unfruitful.

15 What then is it? I will pray with the spirit, and I will pray also with the understanding; I will sing psalms with the spirit, and I will sing psalms also with the understanding;

16 since, if thou mayest bless with the spirit, he who is filling the place of the unlearned, how shall he say the Amen at thy giving of thanks, since what thou dost say he hath not known?

17 for thou, indeed, dost give thanks well, but the other is not built up!

18 I give thanks to my God -- more than you all with tongues speaking --