Does Hebrews 6:4-6 say a believer can lose his salvation?

Hebrews 6:4-6
For it is impossible for those who were once enlightened, and have tasted of the heavenly gift, and were made partakers of the Holy Ghost, 5 And have tasted the good word of God, and the powers of the world to come, 6 If they shall fall away, to renew them again unto repentance; seeing they crucify to themselves the Son of God afresh, and put him to an open shame.

Commonly many point out to this verse and point out believers can lose their salvation if they back slide. I want to tell you the above verses do not refer to believers but the Hebrews who refuse to receive Jesus as their Messiah. 
Note a few verses later the writer addresses the believers as “beloved”. When it comes to them he is fully assured of their salvation. 

Hebrews 6:9
But, beloved, we are persuaded better things of you, and things that accompany salvation, though we thus speak.
See also TNIV
Hebrews 6:9
9 Even though we speak like this, dear friends, we are convinced of better things in your case–the things that have to do with salvation.
The Message
9 I’m sure that won’t happen to you, friends. I have better things in mind for you—salvation things! 

Below are short explanations for each part. It is helpful to note that the letter to the Hebrews is written to Jews and not Gentiles. As such any warnings which are issued are issued to them and not the Gentiles. Let us consider their story in Numbers and Deuteronomy.

The Hebrews stood at the entrance of God’s physical rest –the Promised Land. This was after they witnessed the column of cloud in the day and bright fire in the night; the brightness of His glory on Mount Sinai; and the fire that consumed the rebels. The Hebrews saw His light –they were “enlightened”. (Exodus 13: 21-22, 2 Samuel 22: 7-13, Numbers 11: 1-3)
They ate the daily bread –the manna– that He provided. The Hebrews tasted the food (“heavenly gift”) given from heaven to know about the word of God (Exodus 16: 11-18, 31, Deuteronomy 8: 1-4).The Holy Spirit that rested on Moses (so that he could fairly judge the disputes of the people) was later partaken (shared) with seventy leaders to help carrying the heavy burden. In this way, the people partook (shared) in the Holy Spirit (Numbers 11: 4-6, 10-17). 
They saw supernatural events occur before their eyes –like the sea parting before them so they could escape from slavery and their enemies be destroyed (Exodus 14: 21-28). Those miracles were physical demonstrations of spiritual power yet to come through Jesus.
But even after all of these, those stubborn people deliberately refused to go into the Land –God’s Promised Land of rest. That is what it means “by sinning wilfully” or “keep on sinning” by constantly rejected Jesus as their Messiah. Hence please note it is written towards the unbelieving Jews. It is not a letter written to Jews or Gentiles who already believed.

Be at peace and Shalom. 
~ Simon Yap