They can't. They either walk as a slave of righteousness, or unrighteousness. It's as simple as that.
When indwelt by the Spirit of Christ, a believer is filled by the fruits of the Spirit of God (love), - the fullfilment of law, and this brings out works of righteousness, either seen or unseen - until the day of judgement.
Hello Dcontroversal. You are missing out on some very important things here. It is true - we are justified without having to work for it, meaning - we do not come to the faith and justification before God by observation of law as a way of life and righteousness, as the jews still try to do. The law condemns us, and points us to the only one that can rescue, Jesus Christ.
With Christ, you die to the law, and the ways of unrighteousness, and awaken to righteousness, when filled by the Spirit of Christ. Faith is a fruit of the Spirit - this is very important to understand, - (meaning you will also produce the other fruits.)
Remember that it is written, and told by Jesus Christ himself - that all men will know we are His disciples by the love we have for each other. Remember also that it is possible to have believed in vain, - examples of this is found in the book of James.
God is a powerful God, and the Spirit of Christ within the believer fills the believers with fruits of love, - the fulfillment of law, God whom is love, Himself, - and these fruits produces works, because love is action, and selfless. Jesus says that we are to lay down our lives, as He did for us, and that we are His friends if we do this. It is not possible to be one with Jesus Christ, if you are not walking in righteousness, - because if you do not walk in righteousness, you are walking in darkness, and do not have fellowship with Christ within you - out of sync with the Spirit of God. It is written that "we love, because He first loved us."
So the example you are fighting for - if that person does NO works for 50 years, that person has believed in vain. For you do one or the other, you are either a slave to righteousness, or unrighteousness. If you are a slave to righteousness, you will work the works of love, and your works will in many cases be seen - because love is selfless, and unrighteousness focuses on the self.
Love is not self seeking, but others seeking. Faith must produce good works, (we are created in Christ Jesus unto good works) - because faith is a fruit of the Spirit of God. If you are truly filled with the Spirit of God, you will - "walk even as He walked, and love your neighbor as yourself."
James 2:17-18
17So too, faith by itself, if it is not complemented by action, is dead. 18
But someone will say, “You have faith and I have deeds.” Show me your faith without deeds, and I will show you my faith by my deeds.
The works of God is believing in Jesus Christ, for from the faith in Christ - the fellowship with Christ is found, and when you are full of the fruits of Christ within, - your life will be overflowing also with the "good works we are created to do in Christ Jesus."
Galatians 5:22-23 King James Version (KJV)
22 But the fruit of the Spirit is love, joy, peace, longsuffering, gentleness, goodness, faith,
23 Meekness, temperance: against such there is no law.