molecular niyrogen is very inert chemically.
Answers
It is and it isn't, it all depends on your perspective. there are far more inert gases--helium, neon, etc. Then again, people have made complexes of xenon and krypton, so the question is "how inert is inert?" Nitrogen can be made to react, bacteria do this all the time at regular soil conditions, but for people to do it we require pretty extreme conditions (look up the Born-Haber process for making ammonia on wikipedia).
Usually double and triple bonds are not very stable (because the p orbitals that make up the double and triple bonds don't point towards each other and have poorer overlap), but in the case of nitrogen, it's high electronegativity means that it can stabilize those electrons very well, and therefore those bonds are difficult to break like the. But you could say "oxygen has a higher electronegativity and only one double bond to stabilize but it's still really reactive, it burns things." And you'd be totally right. I can tell you there is not an obvious and simple answer for it, but when something like nitrogen makes up 80% of the atmosphere, it's obviously pretty inert, because otherwise it would have reacted to form something else. It's a tautological argument, but it's still true.
Regardless, one thing that you should know is that these simplest of questions are sometimes the hardest, and your question almost borders on philosophy. So good thinking!