Why are many called, but few chosen?

Many fall short of the calling that God has for their lives because they fail to take guidance from His word, and rely on teaching from man or are bound by the tradition of man. God calls us out of the ways of the world, to resist the things that tempt us to go against God, to put faith before flesh. But how can we do this if we do not have the Holy Spirit? And how can we receive the Holy Spirit if we know nothing about Him?