No matter which sect you subscribe to, prayer takes on a central role in Jewish communal life. Liturgy is an essential component of Shabbat, the festivals, mourning, and many other occasions marked by Judaism. Jewish communities are built around the synagogue, whose espoused primary purpose is prayer. The occasions of the year which see most Jews identify with their heritage are the high-holy days, which are prayer marathons par excellence.
Prayer means different things for different people.
Those with a legalistic bent see it as a fulfilment of a divine command or obligation - no less, and perhaps no more. Strong theistic believers might perceive it as an opportunity to converse directly with a personal, sentient deity. For those to whom community is of utmost importance, it might be understood simply as an arbitrary shared communal activity. The spiritual, Eastern-thinking amongst us, could use it as a repetitive framework for meditation. Prayer's longevity is testament to its relevance for many people in many ways.