I have often said that Conditional Security is as close as you can get to a works-based "gospel" without actually taking the plunge. In order to hold to it, you must contend that either salvation is by grace, through faith, yet that faith can be lost, and therefore salvation with it, or that salvation is, at least in part, by works.
Both of these conclusions are precluded by scripture. The latter, of course, is heresy, pure and simple. As God tells us through Paul, "But even if we, or an angel from heaven, preach any other gospel to you than what we have preached to you, let him be accursed." (Galatians 1:8), and "You have become estranged from Christ, you who attempt to be justified by law; you have fallen from grace." (Galatians 5:4). Furthermore, there is an irreconcilable distinction between grace and works made in Romans 11:6: "And if by grace, then it is no longer of works; otherwise grace is no longer grace. But if it is of works, it is no longer grace; otherwise work is no longer work."
Removing all doubt from this, Paul also tells us "Now to him who works, the wages are not counted as grace but as debt. But to him who does not work but believes on Him who justifies the ungodly, his faith is accounted for righteousness, just as David also describes the blessedness of the man to whom God imputes righteousness apart from works: “Blessed are those whose lawless deeds are forgiven, And whose sins are covered; Blessed is the man to whom the Lord shall not impute sin.”" (Romans 4:4-8).
The objection is often raised to this "then why do we even bother avoiding sin?" Anticipating this objection, scripture actually tells us "What shall we say then? Shall we continue in sin that grace may abound? Certainly not! How shall we who died to sin live any longer in it?" (Romans 6:1-2). It is worth noting that aside from answering the objection, the very fact that this is the objection raised shows that this is what it is teaching. No one would look at a gospel in which one can lose salvation and ask "shall we continue in sin, that grace may abound?" That would be a stupid objection. But it is raised against the Biblical Gospel, because the Biblical Gospel does, in fact, teach that salvation is maintained by faith, and not by works.
See, although a Christian can theoretically stay saved without works, it's literally unfathomable that he would want to. It's like saying a living body shouldn't breathe. Even if you're silly enough to hold your breath for an extended period, eventually you won't be able to help gasping for air. If you can hold your breath for too long, that's evidence that you're actually dead. In the same way, if you can go about your Christian walk without walking as a Christian, that strongly suggests your faith is dead.
This can be seen in James chapter 2, which uses this very analogy. As the body without the spirit is dead, James says, so also is faith without works dead. It's no good looking at a hungry man and saying "I hope you get food". If you really want him to be fed, wouldn't you be willing to feed him?
So let's say you really love God. Do you want to serve Him, or your flesh? Every time you sin, scripture says you grieve the Holy Spirit. But it also tells us you are sealed by Him until the day of redemption. Now, tell me, can anyone open what God shuts? Can anyone shut what God opens? God's power is absolute. If the Spirit seals someone until the day of redemption, they are sealed until the day of redemption. In other words, they can't lose salvation. But you can upset the One who saves you.
Thus, we actually have an unselfish motive to avoid sin. I think we can all agree, it is selfish to do even a good thing if it's for your own benefit. In fact, this is the very criticism Jesus has of the Pharisees. They did good things so they could be seen by men. By contrast, we are told "“Take heed that you do not do your charitable deeds before men, to be seen by them. Otherwise you have no reward from your Father in heaven. Therefore, when you do a charitable deed, do not sound a trumpet before you as the hypocrites do in the synagogues and in the streets, that they may have glory from men. Assuredly, I say to you, they have their reward. But when you do a charitable deed, do not let your left hand know what your right hand is doing, that your charitable deed may be in secret; and your Father who sees in secret will Himself reward you openly. “And when you pray, you shall not be like the hypocrites. For they love to pray standing in the synagogues and on the corners of the streets, that they may be seen by men. Assuredly, I say to you, they have their reward. But you, when you pray, go into your room, and when you have shut your door, pray to your Father who is in the secret place; and your Father who sees in secret will reward you openly." (Matthew 6:1-6).
Of course, one might point out the irony in me citing a passage that promises reward in order to refute the idea that we should obey God for sake of reward. To that, I say that, first, this is only an example. Like a beating drum, scripture distinguishes between the heart of faith and the heart of hypocrisy. But second, because it is a two way street. Doing something good without expectation of reward may nevertheless result in reward.
But we should do good without expectation of reward, simply because it is not the giving of reward that makes a thing good. Rather, it is the goodness of the thing that makes it worthy of reward. When we obey God, we should do so simply because He is worthy of obedience. If God had forgiven our sins, but decided to let bygones be bygones and have our souls annihilated, it would still be good to obey Him. Even if God had provided no avenue for salvation, even if we were 100% destined to pay for our sins in Hell, it would still be good to obey Him. Our faith should tell us that regardless of what God can, might, and will do for us, He is worthy of nothing short of our complete and unwavering devotion.
That means our default should always be obedience. Whether we can lose salvation, ultimately, is irrelevant. What right have we to stand in defiance of the Holy One? What suspends His right to condemn our very first impure thought? If God judged us justly, we could not open our mouths in protest. And if we claim to know that, and especially if we can make such an audacious claim as to love Him, why would salvation even cross our minds?
One reason: Gratitude. As I said, reward is irrelevant, but it is also natural. In His love for us, God unselfishly shed the blood of Christ upon that cross. For us. Not for Him, at least not exclusively. For us. The result of this should be that we, not for our own sake, but for His sake, repent of the very sin that separates us from Him, and enter into a relationship.
A good relationship is a two way street. Parent and child is two way. The parent loves, and unselfishly cares for the child, and in turn, the child loves, and unselfishly obeys the parent. Husband and wife is two way. A husband unselfishly loves his wife, provides for her, even sacrifices himself for her, and in turn, a wife unselfishly loves her husband, submitting to him. Selfishness and love are polar opposites, and so while a relationship with a perfectly loving God will naturally favor us, who are imperfect in love, we should nevertheless seek to purge that selfishness. Therefore, setting Conditional Security aside as the false teaching it is, we should nevertheless seek to honor God in our daily lives, loving Him without condition, as He has done for us.