This is the theme, correct? "Why opposing God appointed authority is tantamount to opposing God himself"!"
Why not slightly change the end of your talk to not focus on "humans", but focus only on Jesus?
"Today as Christians, we follow Jesus. We should be loyal to the pattern Jesus laid out for humans to follow.
And as Galatians 1:8,9 brings out, we do not want to divert from the ORIGINAL good news that Christ taught. We today, just like in Moses day and the 1 st century need to be able to see proof of God approval when we follow any human's lead.
Jesus is the highest authority appointed by God.
Always look to Jesus' example when choosing which course to take, thus avoid any opposition to God."
(Looking forward to hearing how it goes :-)