Salvation is a life-long process. Justification, which most people seem to call being saved, is a one-off that begins a long journey in which our faith is tested and proved. Those who fail the test will not be saved, even though they were justified. In other words, those who were saved by professing faith in the gospel will not be saved if they don't obey God and do his will.
Paul listed some sins he implied genuine Christians would not typically commit (in 1Cor. 6:9-10), saying: “Do you not know that the wicked will not inherit the kingdom of God? Do not be deceived, neither the sexually immoral nor idolaters nor adulterers nor male prostitutes nor homosexual offenders nor thieves nor the greedy nor drunkards nor slanderers nor swindlers will inherit the kingdom of God.”
Apparently, although a new Christian might commit such sins occasionally, it is inconceivable (because antithetical to NT teaching) that a mature Christian would commit them so typically that the person could be classified as an adulterer, for example (1John 3:6). Atheists might try to practice the “Golden Rule”, but the key issue for them on judgment day will be explaining what good reason they had for rejecting God rather than glorifying Him as the One who determines what is good/golden.
As soon as new Christians realize they sinned, they should confess it (1John 1:9a) rather than compound it by trying to hide it or cover it up like Adam and Eve did (Gen. 3:7-8). Whenever a believer acknowledges to God his/her known sins of immoral attitudes and actions, God forgives all sins (1John 1:9b). This means he/she is pleasing rather than grieving God or once again is Spirit-filled (walking in the Spirit) and has a right relationship with Christ Jesus (Eph. 4:30, 5:10 & 18). This spiritual flip-flopping is the phase of instability, and although it is bad, failure to confess promptly is much worse, because it results in chain-sinning or back-sliding, which may be called prodigal if it continues very long (cf. Luke 15:11-32).
Someone who does not hunger and thirst after righteousness (Matt. 5:6) and LGW (Psa. 119:9) needs to reevaluate the sincerity of his/her profession of faith in the Lord. As Paul says (in 2Cor. 13:5), “Examine yourselves to see whether you are in the faith.” The spiritual beauty of God’s truth is as awe-inspiring or attractive as the physical beauty of God’s world for one who has the Spirit/mind of Christ (1Cor. 2:12-16).