how far has modern Christianity strayed from the original message of Jesus Christ?

Jesus Christ is the same yesterday, today and forever and so is His message. The same Christianity that Peter, Paul and the early church practiced is what true believers practice in this modern age. Paul wrote in Galatians 1-

“6 I marvel that you are turning away so soon from Him who called you in the grace of Christ, to a different gospel, 7 which is not another; but there are some who trouble you and want to pervert the gospel of Christ. 8 But even if we, or an angel from heaven, preach any other gospel to you than what we have preached to you, let him be accursed. 9 As we have said before, so now I say again, if anyone preaches any other gospel to you than what you have received, let him be accursed.”

The message of Christ is “the grace of Christ.” Grace is undeserved, unearned, unmerited favour. Anything apart from this is not Christianity.

In essence, there is nothing like modern Christianity. Only Christianity.

As it was in the days of the early church, some church leaders today claim to be for Christ but try to pass off a perversion as the message of Christ. I attended many churches well into my thirties and now I realize that variations of this alien/perverted message was the only thing that was preached throughout that time. We were taught that eternal life is something that we work (obey the law and do good deeds) to earn or deserve. But Christ's message says we who believe posess now eternal life and will never come into judgment-

Christ's message is not that horrid perversion that says: “Now that you are born-again, you have to do your best to be godly (like God) so that you shall not perish but have eternal life in Jesus’ name. This false and deathly doctrine that promotes the attainment of godliness and having eternal life by even a smidgen of human effort has been Satan's message since he first used it to deceive Eve in Eden. Even now, Christ Himself is telling us His message of salvation in John 3-

14 “And as Moses lifted up the serpent in the wilderness, even so must the Son of Man be lifted up, 15 that whoever believes in Him should not perish but have eternal life. 16 For God so loved the world that He gave His only begotten Son, that whoever believes in Him should not perish but have everlasting life. 17 For God did not send His Son into the world to condemn the world, but that the world through Him might be saved."

Christ draws a parallel between how the Israelites that were bitten by snakes (infected with the snake sting) got to escape the sting and its deathly effects and how we who look to Jesus for salvation from sin and death get to “not perish but have eternal life.” But that false and perverted doctrine that is being preached in many places says:

“Look at your snakebite symptoms! Ugh! So terrible. How can you produce such terrible symptoms? Treat your snakebite symptoms by yourself and promise to not produce them again and you will be made whole or else you will burn in hell in Jesus' name.”

Romans 5:19 says- “By one man's disobedience many were made sinners, so also by one Man's obedience many will be made righteous.”

Also see 1 Corinthians 15:56-57 - “56 The sting of death is sin, and the power of sin is the law. 57 But thanks be to God! He gives us the victory through our Lord Jesus Christ.”

The snake sting is a picture of the sinner/old nature that was inherited from Adam by all of his descendants. Trying to keep the law in order to be made whole strengthens this sin nature. As it would have been with the affected Israelites had they depended on their human effort and tried to treat their deathly symptoms by themselves thus ignoring the bronze serpent, carriers of the sin nature will produce acts of sin that lead to death when they focus on trying to obey the law in order to be whole/godly and free from their sins. The law that many are struggling to obey in order to be whole and sins-free causes acts of sin to proliferate- Romans 7:5-

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. 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."

Carriers of the sin/old nature might profess Christ but they are not a new creation in Christ seeing as they do not believe that they have been made eternally righteous by Christ's obedience alone. Trying to be good (like God) in order to attain godliness and to “not perish but have eternal life" is the key trait of the old nature.

How can one stop producing deathly symptoms of snakebite (acts of sin that lead to death) without the snake sting (inherited sin nature) being neutralized? Replace the snake sting with life-giving matter (God’s gift of righteousness to all who believe in Jesus Christ which proceeds from Christ’s obedience and not ours) and the symptoms (acts of sin and a lack of good works) will disappear. The people will be made whole.

Faith without works is dead. We who are under Grace believe this truth to the uttermost and always, we have works to show for our faith. The one with no works to show for his faith has not been made whole; looking utterly to Christ for salvation with no trust or dependence on human effort is how we are made whole. So we get to produce works of faith.

Christ did not call us to be doers of the law. We are called to be doers of the word. The word is the word of faith. The law is not of faith. It is the MINDSET or what we believe about Christ and how we are doing our works that makes the difference between doers of the law and doers of the word. Is it you or is it Christ in you? If it is by your own strength (arm of flesh) that you are good (when Christ says there is none good but God,) it means you cannot claim that “it is no longer I who live but Christ that lives in me.” Such are still living in their own power.

At different times, people have tried to give me credit for being a dedicated Christian, generous, a good parent or for being a hardworking employee and even tried to say that this is why God blesses and saves me from every trial. But I know who I am of myself and apart from Christ in me- I am the worst of sinners. l most selfish! There is none good but God. All who like Peter before he denied Christ, think they are or can be good by themselves would be wallowing in sins and utterly lacking in good deeds were it not for God's mercy. His mercy is the skeleton that keeps man from devolving into the sins-ridden mass of flesh that man is of himself.

Good works are evidences of salvation, not conditions. I cannot number the benefits that the Lord loads me with daily but by Grace and only by God’s Grace, far be it from me to chalk His many benefits in my life down to money that I gave to the needy, my being a witness for Him, my non-existent self-effort at being a good person or my good deeds. Like Peter who realized his folly of trusting himself to not deny Christ, by Grace, I see that none of these things would I be able to accomplish by my own human effort (arm of flesh.) When your believing is right, right living will follow.

“The letter (law) kills but the Spirit gives life" is a very popular Bible verse. With the Spirit of the Lord, it is neither by might nor by power. It is impossible for doers of works of the Law to deceive themselves in this matter: if you knew and believed that it is Christ in you doing the works and not your own might and power, it would be difficult for you to point accusing fingers at others who are still struggling with sin and threaten them with judgment if they don't change. Rather, you would see how helpless man is to overcome sins and produce good works and like Moses who pointed the suffering Israelites to the bronze serpent, point such to Christ who saves from sins and transforms the sinner who truly believes to live right, as you say He is doing for you.

But preachers of that perverted message that promotes dependence on the arm of flesh/human effort at accomplishing their twisted interpretation of “faith without works is dead” keep the flock focused on treating sins and attaining wholeness (godliness aka be like God) through human effort, and away from Christ who is Saviour from sins as it is written of Him in Matthew 1:21-

“She will bear a Son; and you shall call His name Jesus, for He will save His people from their sins.”

The thing is, you can't focus on treating your symptoms (depend on your own arm of flesh/human effort-driven sins-curbing abilities or obedience to law) and simultaneously focus on the bronze serpent on the pole (looking to Christ lifted up for our salvation from sin and death.)

Only by following the latter - stopping our silly efforts to save ourselves from sin and death and looking utterly to Christ for salvation does one get to be made whole; to “not perish but have eternal life.”

Posted a more detailed answer in the comments section.