I feel its this way because seriously speaking, Jesus didn't come to make a new religion nor break the laws and customs practiced but fulfilled them. After his death and ascension many people started to call themselves "Christians" or even "Messianics".
My point is ever since a new religion was formed "Christianity" the church took power.
The Church didn't just "take power." The Church is the vehicle by which we learn the faith handed down by Christ to the Apostles, and the way in which we come to a relationship with Christ. Christ Himself established the Church, and gave His apostles the authority to lead, teach and defend it.
The church changed many things like i.e instead of Saturday being the holy day it was changed to Sunday because Jesus resurrected on this day.
You have to understand, most Christians are Gentiles. We are not beholden to the Mosaic Law. We only keep the commandments of the Old Law that Christ Himself instructed us to keep.
Also keep in mind that, in the beginning, Christians did worship at the synagogues on Saturday, and learn the Old Testament Scripture there. And then on Sunday, they would gather together to celebrate the Eucharist; in other words, to partake of the Body and Blood of Christ. After the Jews kicked the Christians out, however, we moved the whole thing to Sunday, and thus to this very day you have the twofold part of the Divine Liturgy: The Liturgy of the Word, and the Liturgy of the Eucharist.
Secondly, the practiced Jewish holidays e.g Passover. Where in the Bible does it say Saturday to Sunday was to be changed?
It was "changed" due to logistical circumstances. Saturday for many Christians is still a day of rest (just look at the modern weekend), and we honor God not just on the Sabbath, but throughout the week. The Resurrection of Christ, however, is far more important, for by it we have the hope of resurrection and new life with God.
Also, as I'm going to say in a bit, the Jewish Passover is the prototype of Christ's Pascha. With the Jewish Passover, God led Israel out of slavery in Egypt, and to the Promised Land. With Pascha, Christ destroyed death, conquered sin, and we are now able to follow Him from slavery to sin and death, to the promised inheritance and life with God in the Kingdom of Heaven.
I do know Jesus healed and worked on Saturday, but doesn't changing it break the 10 commandments?
Christ laid in the tomb on a Saturday, thus resting on the Sabbath, before He rose from the dead on Sunday. However, as Christ said, there is no excuse not to do good on the Sabbath, and because of this, many Christians decide to work on the Sabbath. In doing so, they seek to give glory to God through their labor.
Or even where in the Bible does it say Easter our Christian holiday is to be celebrated?
I understand its from Jesus' last week but why are we celebrating new things?
Christians celebrate Christ's Resurrection weekly, every Sunday. However, when it comes to the anniversary of His Resurrection, doesn't it make sense to celebrate it with even more gusto? It may not be explicitly stated in the Bible, but it was an organic development within the Christian life.
And frankly, we're celebrating "new things" because new things have happened that have a significant bearing on our salvation. The Jewish Passover was a prototype of Christ's Pascha. The Jewish Pentecost is a forerunner of the Christian Pentecost. Christmas is the celebration of the incarnation of the Son of God, beginning the process of uniting our human nature to His Divine Nature, and the reconciliation of God to man.
Again, the trinity it is from the church why do we follow this?
The Trinity has its roots in the Bible, and it was expressed by the earliest Christians. We believe it because it's part of the faith of the Apostles, and it's the same faith that was handed down to their students, and to the students of the students of the Apostles, down through the ages to this day.
My point is why doesn't the Church stick to what the Bible says instead of fully transforming and creating new rules of its own?
Christians preserved the faith handed down to them by Christ for more than 300 years before the New Testament was codified. The Church canonized the Bible, including those books used by all churches in the Liturgy. I think you need to gain an appreciation of the fact that Holy Tradition does not contradict Holy Scripture. Rather, Holy Tradition is the living, breathing faith and life of Christ's Church, of which Scripture is a part.
Looking at your religion, I really have to ask, are you Eastern/Oriental Orthodox? Or are you one of those types that call yourself "orthodox Christian" because it sounds more legit? This is a serious and honest question, and there is no offense intended.