Many churches and many Christians say that "We don't have to keep the Sabbath. Because it was abolished as it is the law in the old testament." However, the fourth commandment of the Ten commandments is "Keep the Sabbath day holy." Then, is there no need to keep the Ten commandments in new testament?

Let's see the first commandment.
Ex 20:1-3 "And God spoke all these words: "I am the LORD your God, who brought you out of Egypt, out of the land of slavery. ①You shall have no other gods before me."

According to their claims, we can obey other gods because this word, the First commandment, is the law of old testament so it was abolished. Do you think that it makes sense? No at all. Whoever believes in God don't think so. Namely, we should keep the First commandment in the new testament. Then what about the second commandment or the third commandment?

Ex 20 : 4~7 "②You shall not make for yourself an idol in the form of anything in heaven above or on the earth beneath or in the waters below. ... ③You shall not misuse the name of the LORD your God, ... "

Of course, we should obey these words if we believe in God. What about the other commandments?

Ex 20: 12~17 "⑤Honor your father and mother ... ⑥ You shall not murder. ⑦You shall not commit adultery. ⑧You shall not steel. ⑨You shall not give false testimony against your neighbor. ⑩You shall not covet your neighbor's house ... "

Shouldn't we follow these commandments, too? Eventually, there is no commandment that we can neglect from the first commandment to the tenth commandment. Even there are many books in bookstore explaining the importance of the Ten commandments and its meaning. They think that we should keep the Ten commandments saying "The old commandments were abolished."
However, can we say that Ten commandments must be kept 'except' the four commandment?? We can not. That's certainly contradiction. If we don't have to keep the Sabbath, we don't have to keep the other 9 commandments. And If we should follow the other 9 commandments, we also should keep the Sabbath.

Therefore, the insistence that we don't have to keep the Sabbath as it was abolished is wrong insistence. According to the teachings of the Bible we must keep the Seventh day Sabbath until the end.