Remigius of Auxerre
Catena Aurea · Matthäusevangelium 10
But when they deliver you up, take no thought how or what ye shall speak: for it shall be given you in that same hour what ye shall speak. For it is not ye that speak, but the Spirit of your Father which speaketh in you.
How or what, one refers to the substance, the other to the expression in words. And because both of these would be supplied by Him, there was no need for the holy preachers to be anxious about either.