For those struggling to be assured of their salvation/wondering about Heb 6:6
[I wrote this for a post that was deleted before I sent it, so I thought I'd share, in case it encourages someone.]
I was not raised in the faith per se, but went to church as a young teen and did "Christian" things, including memorize Scripture, leading worship services and teach (yes, as a teenager, I'm as flabbergasted how that was able to happen as you are). In all of this time, I would say it was more of a head knowledge/rationalization/cultural thing, not fully a heart, soul, being, truly loving of God and trusting in Him.
Around 16, I decided I wanted to live my life my way, and went hard at that for 2 years. At 18, I was burnt out on it and had destroyed most of my life, or looking at it from God's perspective, I like to say God allowed me to bring about my own ruin. At that point, I understood, like never before, there is no life, no love, no peace apart from God and committed to live as His servant and His true son from that point forward (albeit with lots of mistakes and stumbles along the way).
Before, I characterized my life as wanting more things, more of my dreams and desires fulfilled, and now my singular, controlling desire (again, not saying I'm perfect or walk perfectly in it) is to know God more fully, love Him more deeply, and to serve Him more faithfully. I've had doubts as well, but the more I review the Scriptures and examine the evidence (yes, faith is based on evidence, not merely blind trust) the less and less I've doubted, and I'd say now that I only doubt my limits in understanding of God and His Will, not God Himself or His character. Give me a hypothetical button that would make me live perfectly and truly according to God's Will, I will smash that button down as fast as I possibly can.
If Scriptures like Hebrews 6:6 have you concerned about being able to lose your salvation, or of not being able to be saved, consider my example and look closer at those Scriptures. It says that it is impossible for someone to fall away and then be restored again to repentance. It clearly does NOT say that someone who has fallen away can repent but that repentance is not valid. It says that someone who has fallen away simply could not repent again. IOW the idea that you can receive Grace and Salvation, then lose it and then get it again is a nonsensical idea. If you look at the context you see that the author of Hebrews is teaching basics, not some highly technical manual on loopholes in salvation. Similar passages that often are used by our fears and the Enemy to sow doubt and keep us from assurance of salvation work the same way.
If the Enemy still tempts you to doubt, hear the words of our Savior in John's Gospel, which say the same thing about God's absolute purpose and certainty to save those who believe, over and over, in no uncertain terms; (emphasis and bracketed text mine)
"And as Moses lifted up the serpent in the wilderness, so must the Son of Man be lifted up, that whoever believes in him may have eternal life. For God so loved the world, that he gave his only Son, that whoever believes in him should not perish but have eternal life." John 3:14-16
"Whoever believes in the Son has eternal life; whoever does not obey the Son shall not see life, but the wrath of God remains on him." John 3:36
"Truly, truly, I say to you, whoever hears my word and believes him who sent me has eternal (i.e. forever) life. He does not come into judgment, but has passed from death to life." John 5:24
Jesus answered them, “This is the work of God; that you believe in him whom he has sent.” John 6:29
"All that the Father gives me will come to me, and whoever comes to me I will never cast out. For I have come down from heaven, not to do my own will but the will of him who sent me. And this is the will of him who sent me, that I should lose nothing of all that he has given me, but raise it up on the last day. For this is the will of my Father, that everyone who looks on the Son and believes in him should have eternal life, and I will raise him up on the last day.” John 6:37–40
"Truly, truly, I say to you, whoever believes has eternal life." John 6:47
"My sheep hear my voice, and I know them, and they follow me. I give them eternal life, and they will never perish, and no one will snatch them out of my hand." John 10:27-28
Jesus said to her, “I am the resurrection and the life. Whoever believes in me, though he die, yet shall he live, and everyone who lives and believes in me shall never die. Do you believe this?” John 11:25–26
So my question to you is the same as Christ's: Do you believe this? If so, it is God Who saved you, and God does nothing ineffectively. If you've been saved from sin and given eternal life by Him, you are saved and alive indeed. Note in some of the above that Faith brings fruit/works, so if your "faith" was fruitless, your "faith" was not, according to Jesus, the kind God gives and uses to save us. But if you, trusting in the Goodness of God, love Him and serve Him as Lord, obeying His Word: go in peace, your life is in Christ.