This is an example of the misunderstanding not only of Scripture (and I'm not saying you don't understand it, I'm speaking in generalizations) but of the doctrine of perseverance of the saints, or eternal security.
One of the misconceptions about the doctrine of the perseverance of the saints is that it will lead to “carnal Christians” who believe that since they are eternally secure they can live whatever licentious lifestyle they wish and still be saved. But that is a misunderstanding of the doctrine and what the Bible teaches. A person who believes he can live any way he wants because he has professed Christ is not demonstrating true saving faith.
1 John 2 NASB
3 By this we know that we have come to know Him, if we keep His commandments.
4 The one who says, "I have come to know Him," and does not keep His commandments, is a liar, and the truth is not in him;
Thus is the one described as in danger of being "cut off" from the Vine in Romans 11:20-22. Not because of a loss of faith, but as one never truly grafted in, or poorly grafted in. A graft has two choices, to live or to die. A graft that is poorly done or that is poorly supported will perish. In the perspective of the non-Jew grafted into the Vine, a graft "poorly done" is one that is based strictly on emotion, with no true conviction.
Many of us look at someone who walks the aisle and prays the prayer and say, "Now he/she is saved," but the truth is we don't know that. We can't see the heart, we can't know what God has thought of the confession, as to whether it is true and heartfelt or not. That is required. Also required is growth. A graft that does not take in the nourishment of the plant to which it is grafted also dies, and if a person acts on emotion and does not take in the word of God into his/her heart, and does not make the effort to find out about this faith which he/she has claimed, they are like the seeds scattered on the road. They have joyfully received, but are snatched away by the birds before they can even think about taking root.
Our eternal security rests on the biblical teaching that those whom God justifies, He will also glorify.
Romans 8
28 And we know that God causes all things to work together for good to those who love God, to those who are called according to His purpose.
29 For those whom He foreknew, He also predestined to become conformed to the image of His Son, so that He would be the firstborn among many brethren;
Those who are saved will indeed be conformed to the image of Christ through the process of sanctification.
1 Corinthians 6
9 Or do you not know that the unrighteous will not inherit the kingdom of God? Do not be deceived; neither fornicators, nor idolaters, nor adulterers, nor effeminate, nor homosexuals,
10 nor thieves, nor the covetous, nor drunkards, nor revilers, nor swindlers, will inherit the kingdom of God.
11 Such were some of you; but you were washed, but you were sanctified, but you were justified in the name of the Lord Jesus Christ and in the Spirit of our God.
When a person is saved, the Holy Spirit breaks the bondage of sin and gives the believer a new heart and a desire to seek holiness. There is no way any mere human act can undo the work of God, It is impossible. Therefore a true Christian will desire to be obedient to God and will be convicted by the Holy Spirit when he sins. True Christians will never “live any way they want” because such behavior is impossible for someone who has been given a new nature.
2 Corinthians
17 Therefore if anyone is in Christ, he is a new creature; the old things passed away; behold, new things have come.