“Those who have once been enlightened” most likely refers to the initial illumination that results from a response to the preaching of the gospel, as in Heb 10:32.
Would they practice their Christianity according to the revealed Word of God, or would they adhere to certain Church traditions that the magisterial reformers continued to hold dear and used as a test of orthodoxy in their state-run churches?
The key section of Hebrews 6:1-8 which causes so much angst for preachers is the middle sub-paragraph 6:4-6. Before we can begin to think about how to outline and preach this passage, we must untangle the Greek syntactical structure.
Here are a couple of reasons why I tend to wince at hearing someone bloviate about being “Christ-centered” in preaching, or whatever.
“I can’t wait until all 17 publicly profess their faith in Christ through baptism. Praise the Lord for His grace.”