Your Question got cut off but I want to address that part I have under two headings, looking at the nature of Christian purity and rewards and the present struggle with sin.
Christian Purity and Rewards
The Bible describes believers in Christ as purified or cleaned in Christ (1 Jo 3:3, Heb 9:13). When we describe believers as seen by God ‘as though they have never sinned’ we are talking about this cleansing. It is that the believers conscience is now clear as their sins are forgiven. Christians may be forgiven but will inevitably continue to sin and may never be comfortable with sin. One question is whether Christians, though they are seen as pure by God, will be rewarded for overcoming sin.
At the final Judgement in Rev 20:12-15, we see that men and women’s lives are judged according to ‘the books’ but only those with their names in the ‘book of life’ are permitted into the new heaven and new earth. Rev 21:17 also indicates that it is those whose names are in this book who are the pure. The Christians are still judged according to the books, yet are not thrown into the lake of fire. I think that this is an indication that the Christians will still be judged for their lives but will not be condemned. There are also other indications that Christians will be rewarded at the final judgment based on their lives (Mat 5:12; 6:1-7,18; 16:27; Eph 6:8; Col 3:24), although the nature of this reward is not clear. The ultimate reward is to find that your name is in the book of Christ and recieve an inhertiance with Christ. My inclination is that there is something more as well. 1 Cor 3:14 indicates that some may be rewarded and others not, my inclination is that here there may be the relational reward of seeing others saved, rather than some sort of status.
God will judge the lives of Christians but they will be seen to be saved in Christ. The Bible speaks about rewards in the Kingdom of Heaven for those who do good now and I take it that these verses may be referring to more than mere salvation. The nature of these rewards is not spelled out, but my opinion is that they are related to seeing others there with you in heaven. One reason to struggle with sin is that the character of your life may lead others to Christ and see them saved on the last day.
Struggling with Sin
One underlying issue here is that of Christian Assurance. If you are certain that you are saved why worry about struggling with sin? Why not just give in to sin and let God take care of the forgiveness? Romans 6 addresses this issue, to continue in sin is to deny the freedom we have in Christ. Christians are called not to look back to their old lives, or to the world but to set their hope in Christ.
That is all well and good but when trying to avoid sin is a struggle, it seems easier to just sin and patch things up later with God. Yet this sort of complacency with sin is dangerous. Most people do not decide to suddenly stop being Christian, normally it is the process of a lots of little compromises until one day you no longer find Jesus relevant or worth believing.
Hebrews 10:26 puts the consequences of continuing in sin very starkly:
If we deliberately keep on sinning after we have received the knowledge of the truth, no sacrifice for sins is left, but only a fearful expectation of judgment and of raging fire that will consume the enemies of God.
In this verse sin is seen not so much as a specific act of sin (I can’t help lieing!), but rather a continual rebellion against God which is never repented from (I will continue to lie and I don’t care!). What this does tell us is that to continue to sin is heading the wrong way, it is not the freedom we have been given in Christ but a return to slavery. While Christians can and do sin, sin must not master the Christian (Rom 6). To become complacent about sin in your life as a Christian is profoundly dangerous.
In the Bible God speaks two ways to Christians, those who are complacent about sin are called to repent and those who are deeply worried about their sin are reminded that they are secure in Christ.
Although Christians will always struggle with sin until Christ’s return, in Christ God gives us the gift of righteousness (1 Cor 5:21). To refuse to struggle against the sin in our lives is to go back and wallow in the filth we have been saved from and to run away from the holy God who has saved us and called us to be holy. 1 John is a great book that reflects this tension of sin in a believers life.
At the heart of it, Christians try not to sin because it is better for us not to. God who made us knows the best way for us to live and has given us power through his spirit to begin to live this better way.