​For if we sin wilfully after that we have received the knowledge of the truth, there remaineth no more sacrifice for sins, But a certain fearful looking for of judgment and fiery indignation, which shall devour the adversaries. (Hebrews 10:26-27)

Many say this verse proves that we can lose our salvation.  I used to believe this, as well.  The problem with that interpretation is that if we're to believe it, it also means that, if possible, once we lost our salvation we could never get it back.  And that's a point they neglect to point out.

Another interpretation is that it's absolutely true, there is no more sacrifice for sins after we sin willfully.  But that does not mean Jesus Christ's sacrifice is insufficient to cover our sins.  Believers are still going to heaven and still have Christ's righteousness imputed to their account.

As for the second part, there remain earthly consequences for the believers' sins, and I believe that addresses the fearful looking for judgement and fiery indignation:

• And ye have forgotten the exhortation which speaketh unto you as unto children, My son, despise not thou the chastening of the Lord, nor faint when thou art rebuked of him: For whom the Lord loveth he chasteneth, and scourgeth every son whom he receiveth. If ye endure chastening, God dealeth with you as with sons; for what son is he whom the father chasteneth not? But if ye be without chastisement, whereof all are partakers, then are ye bastards, and not sons. Furthermore we have had fathers of our flesh which corrected [us], and we gave [them] reverence: shall we not much rather be in subjection unto the Father of spirits, and live? For they verily for a few days chastened [us] after their own pleasure; but he for [our] profit, that [we] might be partakers of his holiness. Now no chastening for the present seemeth to be joyous, but grievous: nevertheless afterward it yieldeth the peaceable fruit of righteousness unto them which are exercised thereby. (Hebrews 12:5-11)