“For the Holy Spirit will teach you at that moment what you should say.”
Twice in today’s Gospel passage, God the Holy Spirit is referred to. The first mention is somewhat ambiguous in meaning: in its plainest sense, “blaspheming against the Holy Spirit” would refer to denying that the Holy Spirit is truly and fully God. The Church has had to combat such denial throughout her history.
The second mention of the Holy Spirit refers to a situation that many Christians face at some point in their lives. Whether at the point of death or with the fear of mere embarrassment, Christians at a loss as to how to defend the Faith must rely on the Holy Spirit. Even the most brilliant Christian orator or preacher (St. Augustine of Hippo being a prime example) knows that human brilliance in any measure is dwarfed by, and indeed comes from, the Wisdom of the Holy Spirit.
However, the Holy Spirit teaching the Christian what to say does not mean that the Christian becomes a puppet or megaphone of the Holy Spirit. It is the Holy Spirit who teaches at that moment, but it’s still the Christian who must speak in his own name about the Holy Name of Jesus, making the Good News his own.