Absolutely, and faith in His forgiveness and grace is what brings us INTO a relationship with Him. What I am aiming to prove out, however, is that certain expectations are placed upon the relationship once it is formed, and if not met, can cancel out the grace originally bestowed.
I do understand what you are saying, and I understand that this is a very deep topic that can have many nuances. My objection to the idea that a Christian must essentially work to keep their salvation and is under the threat of being booted out of God's grace if he doesn't perform as he should, is two...no, three things. The first would be the whole meaning of 'Grace' in the first place. The other two would be these verses:
Let me ask you only this: Did you receive the Spirit by works of the law or by hearing with faith? Are you so foolish? Having begun by the Spirit, are you now being perfected by the flesh? -Galatians 3:2–3
All that the Father gives me will come to me, and whoever comes to me I will never cast out. For I have come down from heaven, not to do my own will but the will of him who sent me. And this is the will of him who sent me, that I should lose nothing of all that he has given me, but raise it up on the last day. For this is the will of my Father, that everyone who looks on the Son and believes in him should have eternal life, and I will raise him up on the last day.” -John 6:37–40
So, to my mind, while there can be conversations over Romans 6 and the meanings on what it means to slip back towards sin, I just can't see how we can dance around the clear directives in these two passages. Paul insists that initial salvation is by the 'Spirit' with faith, and that sanctification...'being perfected' must be the same...that trying to do so 'in the flesh', which is works, cannot be done. In fact, he calls it foolish!
Then Christ tells us that those who God has determined to be Christs WILL be Christ's. And Christ will not let them go or turn them away. He WILL raise them up on the last day. And that tells us what? That it is NOT by our works, which are imperfect, but by the work of Christ, which is both perfect and sure. It is by his strength, his perfection, his works, that we are raised up on that last day, just as we are saved.
Take for instance the analogy in our text. The slave who does not turn to obeying his new master but continues to serve the old one (in this case, sin) will not please his new lord. In fact, it will end the relationship between them, and in the worst possible way.
This is what I believe Paul was communicating in verse 16, and why he said the wages of sin is death:
16 Do you not know that to whom you yield yourselves slaves to obey, his slaves you are to whom you obey; whether [as a slave] of sin unto death, or [as a slave] of obedience unto righteousness?
I think there is a problem with ONLY holding to the slave analogy. While this passage certainly uses it, it's not the only one we see when the bible talks about the new status of the believer, and I think its important to link it in to this conversation to get the whole picture. The bible calls us adopted sons of God. We must also remember that the slavery in the bible is different than the sort of slavery that comes to our mind when we hear the word; its not the sort that happened in America back when. Biblical slavery wasn't the stealing of a person and forcing them into a life of forced labor. It was more when a person couldn't pay their debts they would agree to work them off by becoming that person's employee. They would have the same rights of other employees, they just had to stay until the debt was paid off. So, when we see the bible saying that we are rescued from slavery to sin and are now free to become slaves to righteousness, we add that to the picture of our adoption as sons of God. In affect, the picture that's being built for us is that situationally we've just been moved from indentured 'slave' to living in the masters house as 'son', with all the benefits that come with that.
So when Paul then calls us not to fall back into enslavement to sin, he saying how foolish it would be to be living 'the high life' but to get up each morning and trudge back off to work under the harsh eye of the foreman. We are needlessly experiencing the effects of our 'old life', rather than embracing the new.
However, I do not think that the text, or Paul, infers that a Christian, an adopted son of God, even acting in such a foolish and blind manner, gets 'un-adopted'. Any adopted child who lands in a really good, loving family will come to tell you that it didn't matter how they 'stuffed up', that family called them their own and welcomed them with open arms, even after they had done foolish things. This is how we must understand our adoption. We will all do foolish things. We will all slide backwards towards sin at times. But the God who sent his Son to die for us so we might become sons of God when it was obvious we could not get into the family by ourselves, does not then punish us for the same weakness. He encourages us to be better, he helps us to BE better by his Spirit. But he does not turn us away.
I was also pointing to the parable of the unforgiving debtor in my previous post. Here again the debtor is forgiven purely by grace, but thereafter expectations are placed upon the relationship. The lord expects the debtor to go and show others the same mercy he was shown. When these expectations are violated, the relationship is severed and the grace is rescinded.
But...are we to understand that the original man begging for his debts to be forgiven was truly a Christian? We know from other scriptures that there will be plenty of people who have 'called on the Lord' falsely. And that we know that not only on the Last Day, but by their fruits. And clearly, this man, having believed that everything was 'hunky dory' with his own debts, then turned around and showed the most rotten of fruits.
I think rather than showing that Christians must work to keep their salvation and are punished for not bearing good fruit, which I think is an idea contradicted by other passages (see above), it shows the folly of people sitting self-righteously in church, or wherever, believing them and God to be 'good', but then living a life completely not in step with a person who truly received grace.
So too, in the parable of the talents, you have very clear expectations. The one who received the one talent received something from his lord, so this suggests that a relationship was established. But the servant in this relationship was then clearly expected to go and work with what was given to him by his lord's grace, so as to create more wealth out of what he had. When the servant did not do this, the grace was rescinded and the relationship severed.
There are others I could cite which follow the same pattern, but the one I wanted to focus on was the first one, since it is implied in the passage brought up in the OP.
Again...I'm not sure I would interpret that parable strictly in that light. So...in the parable we see two servants go out and work with what their master gave them, right? They are most pleased to use what their Master has given them. The third, however, is not. He doesn't like his master, in fact he claims he's scared of him. That could be true, or he could just be a lazy bum who's making excuses. Either way, he does nothing and then tries to blame it on the master, who rightly punishes him.
Now, I would suggest that rather than being a parable about the woes of not working for your salvation, it's a parable that highlights the heart and spirit of those who are saved versus those who are not. The two who are happy to take what their master; Christ, has given them, and work with them, is those who have new hearts. As James tells us in his book, faith is not a true faith unless it is accompanied by works. It's DOING stuff for Christ that evidences our new hearts. And it doesn't really matter if we stuff up, or if its big or small or we struggle with it, what matters is it will be there, and it will be growing. The third servant? Well, that man was clearly dead. He wanted nothing to do with his master or the talent his master gave him. According to James, this man is not saved.
That's how I'd take this parable.