John Calvin Commentary Acts 8:10

"to whom they all gave heed, from the least to the greatest, saying, This man is that power of God which is called Great." — Acts 8:10 (ASV)

For the title, great power, tends to this end, that whatever might otherwise be divine might become vile through this greatness. Therefore, the power of Christ appears more plainly by this, in that Philip broke through these hindrances, which Luke amplifies.