Falling (away) from Grace (Part 1)
Hebrews 6:4-6 must be evaluated in the context of 5:11-6:20. While many teach and preach and believe this passage declares that our salvation is a tenuous arrangement with God, such is not the case when the context is carefully considered.
Building a theology based upon snippets of Scripture is sure to lead to confusion and play into the enemy's hands. Making this mistake with Hebrews 6:4-6 probably creates more doubt about our standing as Believers with our Heavenly Father than any other passage of Scripture.
What is the bottom line? This passage is discussing spiritual growth and maturity, not salvation. It would be wise to review this part of Hebrews for yourself:
Hebrews 6:4-6
Hebrews 5:11-6:20
While repentance, faith, instruction, judgment, holy living, etc. are noteworthy and valid for discussion and analysis by Believers, these are the elementary things of the Word. In other words, these are the milk of the Word—the basics—while the message of God's grace and the "word of righteousness" (5:13) is the solid food of the Word.