The Greek word is an adjective used as a substantive (noun) within a prepositional phrase εἰς τὸ παντελὲς. An adjective can be only gender. The neuter is used for adverbial use. Thus, the prepositional phrase modifies the verb σῴζειν ... δύναται
(able to save) which encloses the phrase to make sure you take it that way.
πας means all
τελος has the idea of bringing to an end, finishing, or completing
The word in the Torah having this idea of completing atonement is שָׁלֵם. It is used to mean restitution has been completely made. Thus, while the meaning includes forever, it is not limited to that meaning. It means completely restored from the penalty of sin. It means complete restitution for all time has been made.
The Hebrew noun is שָׁלוֹם (peace) and this complete salvation is expressed in Col. 3. Peace of Christ means wellbeing, a complete, whole person in Christ.
And let the peace of Christ rule in your hearts, to which indeed you were called in one body. And be thankful.
(Col. 3:15, ESV)
Note the full context of Col. 3 what to put on and take off and also the verses that follow.
In Hebrews note:
For the moment all discipline seems painful rather than pleasant, but later it yields the peaceful fruit of righteousness to those who have been trained by it.
(Heb. 12:11, ESV)
Now may the God of peace who brought again from the dead our Lord Jesus, the great shepherd of the sheep, by the blood of the eternal covenant, 21 equip you with everything good that you may do his will, working in us that which is pleasing in his sight, through Jesus Christ, to whom be glory forever and ever. Amen.
(Heb. 13:20–21, ESV)
Appendix
This word is used only one other place in the New Testament:
And behold, there was a woman who had had a disabling spirit for eighteen years. She was bent over and could not fully straighten herself.
(Luke 13:11, ESV)
παντελής, ές (trag., Hdt.+; inscr., pap.; 3 Macc 7:16) (quite) complete, perfect, absolute εἰς τὸ π. for the adv. παντελῶς (Philo, Joseph., Aelian). It can mean
- the same thing as παντελῶς, i.e. completely, fully, wholly. ...
- at all; so Lk 13:11, if εἰς τὸ π. is taken w. μὴ δυναμένη instead of w. ἀνακῦψαι she could not straighten herself up at all ...
- of time: forever, for all time ...
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Arndt, W., Gingrich, F. W., Danker, F. W., & Bauer, W. (1979). A Greek-English lexicon of the New Testament and other early Christian literature : a translation and adaption of the fourth revised and augmented edition of Walter Bauer’s Griechisch-deutsches Worterbuch zu den Schrift en des Neuen Testaments und der ubrigen urchristlichen Literatur (p. 608). Chicago: University of Chicago Press.
Wherefore (ὁθεν [hothen]). Since he alone holds this priesthood. To the uttermost (εἰς το παντελες [eis to panteles]). Old idiom, in N. T. only here and Luke 13:10. Vulgate renders it in perpetuum (temporal idea) or like παντοτε [pantote]. This is possible, but the common meaning is completely, utterly.
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Robertson, A. T. (1933). Word Pictures in the New Testament (Heb 7:25). Nashville, TN: Broadman Press.
שָׁלֵם ... vb. be complete, sound ...
- be complete, finished, ended ...
- be sound, uninjured, ...
- make whole or good, restore thing lost ...
- make good, i.e. pay, vows, ...
- requite, recompense, reward, good ...
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Brown, F., Driver, S. R., & Briggs, C. A. (1977). Enhanced Brown-Driver-Briggs Hebrew and English Lexicon (p. 1022). Oxford: Clarendon Press.
שָׁלוֹם ... n.m. Is 54:13 completeness, soundness, welfare, peace ...
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Brown, F., Driver, S. R., & Briggs, C. A. (1977). Enhanced Brown-Driver-Briggs Hebrew and English Lexicon (p. 1022). Oxford: Clarendon Press.