“I will also speak of your testimonies before kings, and shall not be put to shame.”
David most likely did this before Saul, the King of Achish, and the Princes of the Philistines all before he became King. And when he was a King himself, when other Kings came to visit him, instead of talking only about the affairs of the state, he probably spoke of God’s testimonies.
This is how our lives need to reflect God’s glory. Not everyone is called to be in the ministry full-time. But, we are all called to be using the various positions we have been given in our families, at work, with our kids activities, and with our neighbors to share the gospel.