As I read on mi yodeya, that following the 613 mitzovet is a nessesary for righteous jews, and I also know that this task is very difficult, but the seven mitzovet of Noahich laws are easy, and the I know that the follower of the 613 mitzovet will definitely have a portion in Olam Haba and the person who is gentile and following the seven noahiche laws will also have portion in the Olam haba, then my question is , Why to not follow the seven laws of Noaha, these laws are easy and after that there is no binding to follow any thing, and after all the follower of the 613 mitzovet and the bne noahaich both will have good portion in olam haba, then why we should put ourselves in more pains by following the 613 mitzovets, I am sorry if some thing wrong in my question, I just want to ease my mind.
If I interpret this question correctly, it is based on the misconception that a person becomes a Jew and therefore obligated to keep 613 mitzvot by virtue of adopting the Jewish creed, just as a person would, lehavdil, become a Christian by virtue of adopting the Christian creed.
Actually, being a Jew, in this sense, is a matter of nationality rather than of belief. One is a member of the Jewish Nation and therefore obligated to keep all of the Mitzvot, if either one is born of a Jewish mother or one undergoes a "conversion" process. This conversion is more like becoming a citizen of a new country than simply adopting a belief system. People who are members of this nation through one of these two avenues are made responsible by God, whether they like it or not, to fulfill the 613 mitzvot.
Now, the argument that you make is certainly a valid one - to someone who is considering conversion to become a Jew. In fact, it is one of the arguments that any rabbi the potential convert approaches will pose to that person: Why adopt more responsibility? Why not just be a really good follower of the laws you're already obligated in?