This is generally not true. Try to replace "Christian" with "Atheist" or "Gnostic" and see how far this travels. While there are, I suppose, some distinctive practices that characterize various systems of belief (or disbelief), what distinguishes Christianity from, say, Judaism, is a set of irreconcilable beliefs (e.g., that Jesus of Nazareth is the Messiah). It is true that practices might distinguish religious groups (e.g., Orthodox Jews eat no pork, which is allowed to Christians), but those practices directly correlate to beliefs (Peter, citing Jesus, declares all meats clean in the New Testament).
No, religions are not merely practice: they are creedal, too. One who rejects the virgin birth is per se not Christian, at least if the word "Christian" means anything.
This is an excellent example of how Christians take one or a few verses out of context and let them tell a story. If you would read the full passage about Peter, you’d find that the meaning of it was that whatever Gd has made clean shouldn’t be declared unclean by man. He goes on to explain it by saying that the Jews in his time weren’t allowed to go to a gentile, but, because Gd never said (when you study the Pentateuch) that any man was either clean or unclean (except certain circumstances), Peter shouldn’t consider gentile unclean by them being non-Jew.
Much of this reasoning applies to Christians when explaining that Jesus freed them from the law (eating pork, keeping Shabbat, etc), by which they basically support the questioning of Him being the Messiah. Anyone who proclaims to not follow the law, cannot be the Messiah (Deuteronomy 18:20).
However, if you’d read the NT carefully, combined with the scriptures of the scholars of that time (Hillel, Shammai, Gamaliel and more), you’d find that he’s a law obeying person, and encourages everyone to do so. Even stronger; He has much of the same understandings that the rabbis of his time have.
An example is Talmud (Shabbat 31a) where Hillel is asked to tell the Torah when the listener is standing on one foot. He answered by saying: What is hateful to you, do not do to your neighbour. That is the whole Torah; the rest is the explanation of this—go and study it!
This is remarkably similar to what Jesus said when someone asked Him, and Jesus responded with something that was in his time spirit, but also written in Leviticus 19:18 (Matthew 22) 36 Master, which is the great commandment in the law? 37 Jesus said unto him, Thou shalt love the Lord thy Gd with all thy heart, and with all thy soul, and with all thy mind. 38 This is the first and great commandment. 39 And the second is like unto it, Thou shalt love thy neighbour as thyself. 40 On these two commandments hang all the law and the prophets.
Also this very passage explains that Jesus didn't get rid of the law, even more so, He said that Love for Gd (in the ways mentioned and taken from the Sh'ma (Deuteronomy 6:4-9)) and love of your neighbour are the base on which you execute every law (and prophets) that's given. Without this base, everything you do is worthless, it's merely a disguise than being a righteous (Tsaddik)
Both creeds and practices do tend to identify differences between religious groups, but those differences may not be so clearly cut in practice. At the same time, various sects may define the boundaries of the religion more narrowly than others.
The scriptures weren't atomized into verses until scholars of the 15th century wanted to work on them. The practice you see today is an outgrowth of that epistemology, and greatly to the detriment of Christian witness, theology, and practice.
But American evangelical Protestants are a small minority of global Christianity. Catholics and Orthodox take a different approach, one which emphasises the binding role of church Tradition in interpreting the Bible, an idea which Protestants reject.
When Luther nailed the famous arguments on the church door (in common German so everyone could read them), he wasn't wanting to start up a new church. He was just pointing out the ridiculousness of buying forgiveness and the insane corruption and tradition over Scripture that had caused it. Instead of fixing the problems, the Catholic church doubled down and claimed the right to supersede even Jesus Himself. When they couldn't justify with words, they went straight to force.
Also keep in mind that the Catholic church was a political machine first and foremost. The Jesuit order in particular was so political that countries actually pushed the Pope so hard he issued Dominus ac Redemptor to completely suppress the entire order. It was rescinded 41 years later, but due to the internal political power of the Jesuit General, the cardinals refused to elect a Jesuit pope. Politically, the election of the first Jesuit pope in 2013 (199 years after the suppression was rescinded) hallmarked a very large political victory and unification of the Catholic church.
With that in mind, the Protestant Reformation, while primarily religious, was also political in nature.
I just had to quote that sentence construction without comment.
But to reply to it more coarsely: who are you to define what a "Christian reading" of the bible is? As I see it, watching from outside the community, the piecewise selective quoting is very much a fundamental part of the practice of Christianity in the modern world -- especially of the evangelical Christianity that dominates in the USA.
I mean, I agree it's dumb. I just don't see why it's not "Christian". Christians are what Christians do.