Yussel,
In Judaism we believe in G-d, but we also believe that Tzaddikim can daven for us because they are closer to G-d than we are. This is plain and simple, why go to kivrei tzaddikim? If you beleive in the Torah and do what Hashem wants from us he will help us in return. The words of tzaddikim stay forever, and Rebbe Shimon said that he will help those who help increase simcha on Lag B’omer! It is in black and white in the zohar!