Is Justification Permanent? Part One

Hello,
In my earlier post on justification, I said that God's justification of sinners is a permanent act. Justification doesn't give us a temporary righteous standing before God, but a permanent one. However, my older sister, Maria, objected to that claim (with a blog comment and an e-mail) based on the passages in the Bible that warn that holy living is necessary in order to enter heaven. I will first reproduce the verses she raised in objection to the permanence of justification before moving on to my response:

Mark 3:28-29 - "Truly, I say to you, all sins will be forgiven the children of man, and whatever blasphemies they utter, but whoever blasphemies against the Holy Spirit never has forgiveness, but is guilty of an eternal sin"

Matthew 6:15 - "but if you do not forgive others their trespasses, neither will your Father forgive your trespasses."

If I have a permanent righteous standing before God, how would these verses (in the future tense) still apply to me?

Luke 12:46 - "the master of that servant will come on a day when he does not expect him and at an hour he does not know, and will cut him in pieces and put him with the unfaithful."

This was a servant of Christ, yet he was unfaithful, so when Christ returned, he was assigned a place with the unfaithful. Likewise, even though we're now servants of Christ, we don't know yet what final places (heaven or hell) we will be assigned when Christ returns.

Revelation 2:5 - "Remember therefore from where you have fallen; repent, and do the works you did at first. If not, I will come to you and remove your lampstand from its place, unless you repent."

Revelation 3:16 - "So, because you are lukewarm, and neither hot nor cold, I will spit you out of my mouth."

Revelation 3:5 - "The one who conquers will be clothed thus in white garments, and I will never blot his name out of the book of life. I will confess his name before my Father and before his angels."

Why would Christ mention that he isn't going to "blot his name out of the book of life" if that's something he wasn't ever going to do anyway?

If our justification were permanent, then we could sin unrepentantly until the day we die and still go to heaven. The Bible clearly says that it doesn't work that way:

Hebrews 5:9 - "And being made perfect, he became the source of eternal salvation to all who obey him,"

Romans 2:7 - "to those who by patience in well-doing seek for glory and honor and immortality, he will give eternal life;"

We can't obey God once and go to heaven, we must continue to obey him as evidence of our love and reverence for him. We can't do good once and get eternal life. We must be persistent in doing good.

And Paul says in Romans that we can lose our standing as heirs of the kingdom of God:

Romans 11:17-22 - "But if some of the branches were broken off, and you, although a wild olive shoot, were grafted in among the others and now share in the nourishing root of the olive tree, do not be arrogant toward the branches. If you are, remember it is not you who support the root, but the root that supports you. Then you will say, 'Branches were broken off so that I might be grafted in.' That is true. They were broken off because of their unbelief, but you stand fast through faith. So do not become proud, but stand in awe. For if God did not spare the natural branches, neither will he spare you. Note then the severity of God: severity toward those who have fallen, but God's kindness to you, provided you continue in his kindness. Otherwise you too will be cut off."

That doesn't sound very permanent to me!

John 14:15 - "If you love me, you will keep my commandments."

On one hand, Jesus died for the forgiveness of our sins. But on the other hand, we need to keep his commandments to receive eternal life.