Matthew 10:20
For it is not you who speak, but the Spirit of your Father speaking through you. The Spirit of your Father — the Holy Spirit — is the divine provision for the trial moment. The disciples will speak, but the speech is from the Spirit; they are instruments of a voice greater than their own. This is not a counsel for unprepared public speaking in general but for the specific situation of trial before hostile authorities. The same Spirit who descended on Jesus at the baptism (3:16) will speak through the disciples in their moments of trial. 1 Peter 4:14 says the Spirit of glory and of God rests on those who suffer for the name of Christ.