How is Modern Christianity different from the forms of Christianity that preceded it?

This is a huge question that can't possibly be answered in this forum. Suffice it to say that modern Christianity ha deviated in many ways from what the Apostles believed and practiced during the first century. It originates in how you interpret the Bible when you read it. The Church has allowed too much of the liberalism found out in society to infiltrate the body of believers. The church can't simply be a reflection of how the surrounding society is. The church must be something that is not of this world, doing things differently, behaving differently, speaking differently. Today's church too frequently does thing just like the world does.

Modern Christianity is very different, I mean comparing some forms of Christianity to each other they are like an entirely different religion. The biggest change in christianity in modern day is less draconian (forgive me I mean no disrespect but this is the only word that comes to mind) The church used to focus on how not doing good deeds or committing sin lead to consequences so it greatly an image for god being a judge rather than a father. And most modern Christian denominations aren't trying to portray their religion this way it is much more about forgiveness and being moral for the sake of being moral rather than consequences if one doesn't follow. The trouble is some christian denominations still seem to stress the consequence of sin and stress things like hell.

Modern "traditional" Christianity has lost a great deal since the time of Christ both in doctrine and authority. However the fullness of the Gospel of Jesus Christ has been restored to the earth through direct revelation.

The basic answer is that modern Christianity has (to varying degrees) adapted itself to the 21st century world.

Of course, "modern Christianity" displays huge diversity. A mainline Methodist or Lutheran church in a small town in North Dakota is a very different place from a Pentecostal church in Uganda, or a Russian Orthodox church, or an Egyptian Coptic church. But what they share in common is an effort to live out a particular interpretation of Christianity in our modern world.

Now if you were to go back some 1600 years, you would find churches that were adapted to the world of late antiquity. Their social and theological concerns, the way they practiced their faith, etc. all reflected what society was like back then, just as 21st century churches reflect society as it is now.

That's the basic answer. Numerous examples and case studies could be given to explain in detail how it works out in specific instances, but I don't feel like writing an essay!

The most intact view of the oldest form of Christianity is in the Catholic and Orthodox churches. Both these religions take pride in keeping the original form of worship alive. You can see that Christians took part in a Eucharist as a way of celebrating Christ's triumph over death.

"But every Lord’s day gather yourselves together, and break bread, and give thanksgiving after having confessed your transgressions, that your sacrifice may be pure. But let no one that is at variance with his fellow come together with you, until they be reconciled, that your sacrifice may not be profaned"-Didache, circa 70 AD

The True Christian Faith is based upon The Fact of God... it is because we know God, and What He has done for each of us personally... that we have The Faith that what God says was, was... what He says is, is... and what He says will come to pass will come to pass....

The True Christian strives to follow the instruction and life example of Jesus The Christ.... Christ taught ONLY The Word and Will of God for man-kind.... and offered his life as an example of how we are to strive to follow............. and that has not changed....

Man's ego, pride, and greed, have led many into practices(forms) that are far astray from the example of Jesus The Christ.... but... The instructions remain as given by God........ any additions have no Authority from God and have no claim to being "Christian"

Less burning of witches. More tolerance of each other. More tolerance of non-Christians. More tolerance of non-Western cultures. Less temporal power. More consiousness of the plight of social classes beneath the ruling classes.

Better understanding of scripture. Better understanding of the personal call to holiness.

Changes to symbols that make more sense to modern culture, changes to liturgy that appeal to modern culture.

Many things are maintained or reinterpreted to make more sense to modern culture.