Why does the Christian doctrine seem so far from the Bible?

As you have said, there are many other things that were part of being God's people that are not required anymore under the New Covenant. This is why you can buy a bible that is just the New Testament - to be blunt, the concept goes - no one cares about the old stuff anymore and so the NT is all I need to read.

The entire Old T. pointed to the New that would be formed in Christ. This was foreknown by God from before He made the 'world'.

...he(Jesus) was foreknown before the creation of the world... 1 Pet 1:20

All the things they did, that you mentioned, are part of the what led up to Christ.

Therefore no one is to act as your judge in regard to food or drink or in respect to a festival or a new moon or a Sabbath day — 17 things which are a mere shadow of what is to come; but the substance belongs to Christ. Col 2:16

They are not now somehow 'wrong', they are replaced by something far grander. The endless sacrifices of OT are replaced by the one sacrifice of Christ (for eg).

Some of the Feast days are still valid today as they have a future component that is yet to be realised. (Some might say they all do, but that is another topic) But they are not a Holy DAY as they once were, but a reminder of the plan of God He has revealed through them.

The bottom line is - we are made righteous not by doing things, but by faith in what Jesus has accomplished for us. We still 'do things', but only as a response to God's spirit in us.

For the law of the Spirit of life in Christ Jesus has set you free from the law of sin and of death. Rom 8:2

Welcome to the site. I'm assuming you are just starting to investigate Christianity. This is a good question, so I'll try to give you a simple answer.

Most of the Bible, which we call the Old Testament, was written for the Jews. It tells the story of their interaction with God, who gave them all sorts of laws and commands to follow. But one of the things he said was that there would be a person who would come who would set them free.

That person is Jesus Christ, and his story is in the later part of the Bible, the New Testament. The New Testament starts with the Gospels, and is the book of Matthew and everything after. Jesus (speaking for God) tells people that the old laws and commands weren't the point. You didn't have to follow all the old laws like circumcision or feast days, but a new law based around love. He gave his life specifically to free us from it. The old law is useful to know about, but the new law supersedes it.

So if you've been reading only the early part of the Bible, you will find a lot of things that Christians don't do. If you read the later part, especially the Gospels (the books Matthew, Mark, Luke and John) you will understand a lot more. I've simplified this a lot, and if there are specific points you don't understand then feel free to ask about them.

The Differences between the Doctrine of Christ and

1 - Circumcision 2 - Feast days 3 - Following the statutes & judgements 4 - Keeping the Sabbath

The four items mentioned in the question pertain to the first humanity, that of Adam and his seed. By a conspiracy involving Serpent, woman and man - in Eden - the first humanity partook, willingly, of the knowledge of good and evil which God had warned would lead to spiritual death, immediately.

As a result, humanity was judged accordingly and, through physical death, was condemned to return to the dust from whence it came, having failed of its purpose : a purpose which, through the immediacy of its failure, it never even discovered what it was, never mind actually rose to that purpose to fulfil it.

This is seen in the concept of the cherubim which appear, in Eden, when humanity fails, and are ‘settled’ to await another opportunity of realisation, an opportunity promised by God when a seed will arise through woman (not man) and will bruise the serpent from above, that is to say, humanity being raised above angelic power in a new creation.

In Christ, there is a new creation, new heavens and a new earth. In Christ there is a New Testament, an ‘everlasting testament‘. In Christ there is redemption. In Christ there is ‘restitution’ as Peter calls it. In Christ there is ‘restoration’ as Paul calls it.

But not a restitution to what was set out in Israel, with sacrifices and feasts and circumcision and a Sabbath. All those things, and many more, were mere pictures set forth on earth, within Israel, as a testimony to the whole world of what would be when that promised seed came, which God promised after the first humanity failed.

The realisation and fulfillment of that promise is the birth of Jesus Christ, born of the virgin Mary. And his subsequent sufferings, death, resurrection and his ascension to the Throne of God in the heavens, above all principalities and powers, seated at the right hand of God, in humanity.

The redemption, the restitution and the restoration are to what was always in the mind of God, ‘before the foundation of the world ', ‘before the mountains were formed' and 'before there was a sea'.

And in that restoration there is a new humanity, born ‘of water and of spirit’, ‘born anew’, ‘born again’, ‘born from above’, ‘born of God’. It is described in each of these different aspects in scripture.

That humanity is subject to Christ, subject to a New Testament, subject to a New Creation.

It is not subject to the first man, Adam. It is not subject to the Serpent.

It is a ‘new thing‘.