There are many methods, to reach the truth. The belief of God, the concept of God - is also one of the methods.
Believe in God is just a path. But it is not a necessity. You can choose something else. Buddha reaches to that ultimate reality without believing in God. He chooses a different path where God is not needed.
You have come to my house. You have passed through a certain street. That street was not the goal; it was just instrumental. You could have reached to the same house through some other street; others have reached through other streets. On your street there may be green trees, big trees; on other streets there are not. So God is just one path. Remember the distinction. God is not the goal. God is just one of the paths.
It is difficult for Christians and Muslims to think how Buddha could attain the ultimate truth, because he never believed in God. It is difficult for Hindus to believe how Mahavira could attain liberation; he never believed in God.
Before the western thinkers became alert of eastern religions, they always defined religion as God centered. When they came upon eastern thinking, and then they became aware that there has been a traditional path, godless path reaching toward truth, they were shocked: it is impossible.
H. G. Wells has written about Buddha that Buddha is the most godless man and yet the most godly. He never believed and he will never tell anybody to believe in any God, but he himself is the suprememost phenomenon of the happening of divine being. Mahavira too travels a path where God is not needed.
The goal is the truth. Some have achieved it through God, so it is okay – believe in God
and achieve the goal, because when the goal is achieved you will throw your belief. So belief is just instrumental. If you don’t believe, it is okay; don’t believe, and travel the path of belieflessness, and reach the goal.