If salvation is to be lost, then it must be lost through disobedience to God. Most who teach an unsure salvation would agree with this. Yet, what degree of sin brings this loss of salvation? Evil thoughts? Bitterness? Murder? Failing to attend church? Failure to pray? What sin or sins cross the line of no return? Again, we must let Scripture be the measure of truth.

In Corinthians, chapter five, a man in the church had taken his father’s wife as his own. Paul states that this is “such fornication as is not so much as named among the Gentiles” (1Corinthians 5:1It is reported commonly that there is fornication among you, and such fornication as is not so much as named among the Gentiles, that one should have his father's wife.
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Yet Paul’s instructions concerning the treatment of this man in 1 Corinthians 5:5To deliver such an one unto Satan for the destruction of the flesh, that the spirit may be saved in the day of the Lord Jesus.
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To deliver such an one unto Satan for the destruction of the flesh, that the spirit may be saved in the day of the Lord Jesus.

Only his flesh was to be delivered to Satan. The spirit was still saved. This matches the description in 1 Corinthians 3:15If any man's work shall be burned, he shall suffer loss: but he himself shall be saved; yet so as by fire.
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If any man's work shall be burned, he shall suffer loss: but he himself shall be saved; yet so as by fire.

You can lose every reward you could have had and yet go to heaven. Why? Because your salvation is based on the work of Christ, not on your own works. Your works, good or bad, neither gain nor lose salvation.

Another heinous sin is blasphemy. Surely if evil sins could remove salvation, this one could.

Yet, in 1 Timothy 1:20Of whom is Hymenaeus and Alexander; whom I have delivered unto Satan, that they may learn not to blaspheme.
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1 Timothy 1:20
See All...  Of whom is Hymenaeus and Alexander; whom I have delivered unto Satan, that they may learn not to blaspheme.

The pattern is the same as that found in I Corinthians, chapter five. Their flesh is delivered to Satan so that their spirits may be saved in the day of Christ.

You cannot lose your salvation by committing these or other terrible sins. You will be judged. You will lose heavenly rewards. But a human spirit once quickened by God must remain quickened. So, in order to lose your salvation, you must commit sins greater than these.