Hebrews Chapter 6

Therefore let us leave the elementary doctrine of Christ and go on to maturity, not laying again a foundation of repentance from dead works and of faith toward God, 2 and of instruction about washings, the laying on of hands, the resurrection of the dead, and eternal judgment. 3 And this we will do if God permits.
4 For it is impossible, in the case of those who have once been enlightened, who have tasted the heavenly gift, and have shared in the Holy Spirit, 5 and have tasted the goodness of the word of God and the powers of the age to come, 6 and then have fallen away, to restore them again to repentance, since they are crucifying once again the Son of God to their own harm and holding him up to contempt. 7 For land that has drunk the rain that often falls on it, and produces a crop useful to those for whose sake it is cultivated, receives a blessing from God. 8 But if it bears thorns and thistles, it is worthless and near to being cursed, and its end is to be burned.

9 Though we speak in this way, yet in your case, beloved, we feel sure of better things—things that belong to salvation. 10 For God is not unjust so as to overlook your work and the love that you have shown for his name in serving the saints, as you still do. 11And we desire each one of you to show the same earnestness to have the full assurance of hope until the end, 12 so that you may not be sluggish, but imitators of those who through faith and patience inherit the promises.

13 For when God made a promise to Abraham, since he had no one greater by whom to swear, he swore by himself, 14 saying, “Surely I will bless you and multiply you.” 15 And thus Abraham, having patiently waited, obtained the promise. 16 For people swear by something greater than themselves, and in all their disputes an oath is final for confirmation. 17 So when God desired to show more convincingly to the heirs of the promise the unchangeable character of his purpose, he guaranteed it with an oath, 18 so that by two unchangeable things, in which it is impossible for God to lie, we who have fled for refuge might have strong encouragement to hold fast to the hope set before us. 19 We have this as a sure and steadfast anchor of the soul, a hope that enters into the inner place behind the curtain, 20 where Jesus has gone as a forerunner on our behalf, having become a high priest forever after the order of Melchizedek.
ESV
Therefore, leaving the discussion of the elementary principles of Christ, let us go on to perfection, not laying again the foundation of repentance from dead works and of faith toward God, 2 of the doctrine of baptisms, of laying on of hands, of resurrection of the dead, and of eternal judgment. 3 And this we will do if God permits.
4 For it is impossible for those who were once enlightened, and have tasted the heavenly gift, and have become partakers of the Holy Spirit, 5 and have tasted the good word of God and the powers of the age to come, 6 if they fall away, to renew them again to repentance, since they crucify again for themselves the Son of God, and put Him to an open shame.
7 For the earth which drinks in the rain that often comes upon it, and bears herbs useful for those by whom it is cultivated, receives blessing from God; 8but if it bears thorns and briers, it is rejected and near to being cursed, whose end is to be burned.
A Better Estimate
9 But, beloved, we are confident of better things concerning you, yes, things that accompany salvation, though we speak in this manner. 10 For God is not unjust to forget your work and labor of love which you have shown toward His name, in that you have ministered to the saints, and do minister. 11 And we desire that each one of you show the same diligence to the full assurance of hope until the end, 12 that you do not become sluggish, but imitate those who through faith and patience inherit the promises.

13 For when God made a promise to Abraham, because He could swear by no one greater, He swore by Himself, 14 saying, “Surely blessing I will bless you, and multiplying I will multiply you.”15 And so, after he had patiently endured, he obtained the promise. 16 For men indeed swear by the greater, and an oath for confirmation is for them an end of all dispute. 17 Thus God, determining to show more abundantly to the heirs of promise the immutability of His counsel, confirmed it by an oath, 18 that by two immutable things, in which it is impossible for God to lie, we might have strong consolation, who have fled for refuge to lay hold of the hope set before us.
19 This hope we have as an anchor of the soul, both sure and steadfast, and which enters the Presence behind the veil, 20 where the forerunner has entered for us, even Jesus, having become High Priest forever according to the order of Melchizedek.
NKJV
Chapter 6
Therefore let us leave the elementary doctrine of Christ and go on to maturity, not laying again a foundation of repentance from dead works and of faith toward God, 2 and of instruction about washings, the laying on of hands, the resurrection of the dead, and eternal judgment. 3 And this we will do if God permits.
We are not the Heberws

It easy to forget that we are not the original recipients of this letter.  The name of the book is Hebrews, so it should not be a shock to us that it talks about Hebrew things
Washings:

Matthew 15:1-3 Then Pharisees and scribes came to Jesus from Jerusalem and said, 2 “Why do your disciples break the tradition of the elders? For they do not wash their hands when they eat.” 3 He answered them, “And why do you break the commandment of God for the sake of your tradition?
Laying on of Hands:

Leviticus 16:21-22
Aaron shall lay both his hands on the head of the live goat, confess over it all the iniquities of the children of Israel, and all their transgressions, concerning all their sins, putting them on the head of the goat, and shall send it away into the wilderness by the hand of a suitable man. 22 The goat shall bear on itself all their iniquities to an uninhabited land; and he shall release the goat in the wilderness.
Application:

In what ways do modern Christians "go back" to dead works of religion?
4 For it is impossible, in the case of those who have once been enlightened, who have tasted the heavenly gift, and have shared in the Holy Spirit, 5and have tasted the goodness of the word of God and the powers of the age to come, 6 and then have fallen away, to restore them again to repentance, since they are crucifying once again the Son of God to their own harm and holding him up to contempt. 7 For land that has drunk the rain that often falls on it, and produces a crop useful to those for whose sake it is cultivated, receives a blessing from God. 8 But if it bears thorns and thistles, it is worthless and near to being cursed, and its end is to be burned.
Filters:
The danger we all have when looking at difficult scriptural passages is the filter we bring with us.  When photography meant film and processing, I had a set of filters for my camera.  I have a pair of amber tinted sun glasses they make the sky look bluer and add contrast to the clouds, I love them, but am I experiencing the sky accurately. Calvinists and Arminians are both bringing filters to this passage.
Chuck Smith:
What this passage is certainly not teaching is that if you fall into sin, you can never repent.  That is contrary to what the Bible teaches and would leave us all lost.
Michael S. Heiser, Supernatural: What the Bible Teaches about the Unseen World And Why It Matters
“Salvation is not gained by moral perfection. It is a gift that comes by grace, through faith (Eph. 2:8–9). That in turn means salvation cannot be lost by moral imperfection. What is not at all gained by performance cannot be lost by poor performance. Salvation is about believing loyalty—trusting what Jesus did to defeat Satan’s claim and turning from all other gods and the belief systems of which they are a part."
The warning against apostacy should give all of us pause.  It should not be filtered by church tradition.

First, falling into sin, even if it means you've gone to a dance or the movies or played cards, does not mean you've "lost" your salvation.  Look above, "What is not at all gained by performance cannot be lost by poor performance".

This does not mean I agree with Calvinist. I believe in mankind's freewill.  If man can respond to call of the Holy Sprit, then man can later deny that call, however unlikely that seems to me.  I believe that Salvation is dependent on Believing Loyalty.

Second, Imposable? Think about the story of the Rich Young Ruler.
" 24 Jesus, seeing that he had become sad, said, “How difficult it is for those who have wealth to enter the kingdom of God! 25 For it is easier for a camel to go through the eye of a needle than for a rich person to enter the kingdom of God.” 26 Those who heard it said, “Then who can be saved?” 27 But he said, “What is impossible with man is possible with God.” Luke 18:24-27 ESV
With man salvation is impossible.  If you can't save yourself, Jesus can,  If you can't bring yourself back, God can.   If you are worried that you've lost your salvation, you didn't.

Romans 10:9 …if you confess with your mouth the Lord Jesus and believe in your heart that God has raised Him from the dead, you will be saved." NKJV
Pastor David Guzik:
9 Though we speak in this way, yet in your case, beloved, we feel sure of better things—things that belong to salvation. 10 For God is not unjust so as to overlook your work and the love that you have shown for his name in serving the saints, as you still do.
Reuben Welch A Bible Study on Hebrew, Faith for the Journey:
"The situation is hypothetical.  The writer [of Hebrews] is sure that he is not describing the circumstances of his readers; theirs are 'better things that belong to salvation' [Hebrews 6:9].  But the warning is real, and the results of apostasy are awful. The word of [Hebrews 2:3] is heard again: 'How shall we escape if we neglect such a great salvation?'"
11And we desire each one of you to show the same earnestness to have the full assurance of hope until the end, 12 so that you may not be sluggish, but imitators of those who through faith and patience inherit the promises.
13
For when God made a promise to Abraham, since he had no one greater by whom to swear, he swore by himself, 14 saying, “Surely I will bless you and multiply you.” 15 And thus Abraham, having patiently waited, obtained the promise. 16 For people swear by something greater than themselves, and in all their disputes an oath is final for confirmation. 17 So when God desired to show more convincingly to the heirs of the promise the unchangeable character of his purpose, he guaranteed it with an oath, 18 so that by two unchangeable things, in which it is impossible for God to lie, we who have fled for refuge might have strong encouragement to hold fast to the hope set before us. 19 We have this as a sure and steadfast anchor of the soul, a hope that enters into the inner place behind the curtain, 20 where Jesus has gone as a forerunner on our behalf, having become a high priest forever after the order of Melchizedek.
We have a promise from God which is just as sure as the promise Abraham received.

We have Jesus as a high priest after the order of Melchizedek, which we will encounter much more in chapter seven.