Answer: The whole Book of Hebrews is a contrast between the Old Testament Law and the New Covenant made upon Calvary by our Savior, the Lord Jesus Christ. Chapter 10:1-18 continues the contrasts.
In Verse 19, Paul addresses those who are saved as "brethren." In Verse 23-25, instructions are given to the saved to follow, so they can grow in strength through the grace and knowledge of the Lord Jesus. (2 Peter 3:18). Paul, then, instructs the believers, in Verse 23, of the importance of remaining faithful. In Verse 24, he advises them of the importance of considering others and encouraging them to do the same. In Verse 25, he instructs them of the importance of "not forsaking the assembling of yourselves together."
In Verse 26, the subject changes. Paul is now speaking concerning his Jewish brethren (i.e. in the flesh, not the Spirit), and identifies himself with them when he was without Christ.
Since Jesus Christ is "the way, the truth, and the life: no man cometh unto the Father, but by me."... He then presented Himself unto Israel first. John 1:11 tells us that,
"He (Christ) came unto his own, (Israel) and his own (Israel) received him not."
Paul, in Verse 26, is telling His Jewish brethren after the flesh, who are unsaved, that "If they reject Jesus Christ as their payment for sin; there is no other payment for sin. Therefore, there is no other sacrifice for sins." In Verses 27-31, Paul informs those who reject Christ what they have to look forward to when they die.
Now! In Verses 32-39, Paul reminds those Jews, who have received Christ as their Savior, to continue on in serving the Lord.
In Verse 39, the word "perdition" in the Greek means "To utterly destroy." The idea is not extinction; but ruin, loss; not of being; BUT of well-being". The word is used of both the saved and the lost. Also, the word "soul" is the same Greek word as "life" in many cases. For example: In Matthew 16:25, "life" is used twice. In Matthew 16:26, the word "soul" is used twice. All four are the same Greek word.
Verse 39 would literally read,
"But we (the saved) are not of them who draw back (from serving the Lord) unto perdition, (i.e. ruining our life); but of them that believe to the saving of the soul (life)."
Saving our life for what? To use to bring glory and honor to our Wonderful Savior, the Lord Jesus Christ, and to receive His present blessings and future rewards for being faithful.