By my Spirit to direct and assist thee what and how to speak. Whence Moses, though he still seems to have remained slow in speech, yet was in truth mighty in words as well as deeds, Acts 7:22. Compare Matthew 10:19,20.
Related Commentaries of Exodus 4:12
Exodus 4:12
12 Now therefore go, and I will be with thy mouth, and teach thee what thou shalt say.