A.T. Robertson Commentary Mark 16:17

"And these signs shall accompany them that believe: in my name shall they cast out demons; they shall speak with new tongues;" — Mark 16:17 (ASV)

They shall speak with new tongues (γλωσσαις λαλησουσιν [καιναισ]). Westcott and Hort put καιναις (new) in the margin. Casting out demons we have seen in the ministry of Jesus. Speaking with tongues comes in the apostolic era (Acts 2:3f.; 10:46; 19:6; 1 Corinthians 12:28; 14).