How does a person become a sinner?

Believers, Romans 5:19 says "For as by one man's disobedience many were made sinners, so also by one Man's obedience many will be made righteous."

From the above verse, we see that committing acts of sin is not what make people sinners. People are made sinners through Adam's sin. Acts of sin are simply products of having the sinner nature that is inherited from Adam. Sinners will sin, much like how a Managing Director of a company has to manage the activities of his organisation. He might do some cleaning of his surroundings or relocate say a stray mop to its right position sometimes, but that does not make him a janitor. Unless a higher authority changes his designation and job description, he will remain the Managing Director, even when he does something outside his job description.

In essence, no matter how many good things a person does or how well he keeps the Ten Commandments, without receiving our Lord Jesus' blood-bought righteousness which is given as a gift to all who believe Him, he can never be righteous. He has the old (sinner) nature. The end is death.

By the same token, acts of righteousness cannot make people righteous. Many people who are not believers do their best to do only good things. People are made righteous by "one Man's obedience," Christ's, when they believe that God "...made Him who knew no sin to be sin for us that we might become the righteousness of God in Him." 2 Cor. 5:21. Here, we are a new creation in Christ. The old (sinner) nature is no more.

Christ died to make us righteous. If one is trying to keep the law and is doing "good things" in order to get right with God, that one has rejected the gift of right-standing with God that Christ died that we might have. That one has the old (sin) nature that was inherited from Adam by all mankind, and this is the result according to Romans 7:5- 

"When we were controlled by our old nature, sinful desires were at work within us, and the law aroused these evil desires that produced a harvest of sinful deeds, resulting in death."

The very law that such who try to be righteous by their own effort try to keep arouses evil desires in them! Believers, let's not be found here. Sin has dominion over those who are under law.

Also, 1 Corinthians 15:56 says "...the strength of sin is the law."

When one believes in keeping the law and being good in order to gain favour from God, sin strengthens its grip over that one's life. Christ died to make us right with God so thinking that our own good deeds is what makes us right with God is denying the finished work of Christ and its efficacy! This is unbelief.

But when you receive the abundance of grace and believe that you are made righteous by the obedience of Christ (Romans 5:19) and not your own obedience, you no longer have the old nature. You are dead to the law. Old things have passed away. No more curse. You are a New Creation in Christ Jesus. And this is the result according to Romans 7:4-

"So, my dear brothers and sisters, this is the point: You died to the power of the law when you died with Christ. And now you are united with the One who was raised from the dead. As a result, we can produce a harvest of good deeds for God."

Grace is undeserved, unmerited favour. If one iota of our strength is in it, it is no longer Grace (Romans 11:6,) and only by grace through faith are we saved, so we have nothing to boast of in ourselves (Ephesians 2:8-9,) not our own fasts, self-discipline, giving, morality, evangelism, dedication or right-living prowess. With the Lord as our righteousness, "all these things shall be added unto you." We get to be transformed to the image of His glory, from glory to glory, through no effort of ours. We get to love proclaiming Jesus.

Romans 5:17 says: "For the sin of this one man, Adam, caused death to rule over many. But even greater is God’s wonderful grace and his gift of righteousness, for all who receive it will live in triumph over sin and death through this one man, Jesus Christ."

Only with Christ as our righteousness do we live in triumph over sin. 

The Holy Spirit will teach you all things.

Believe Right and you will Live Right.