HOW CAN I BELIEVE IN SOMETHING THAT I CAN’T SEE?

Answer:
When Moses asked to see God’s glory, God told him, "I will make all my goodness pass before you,...[but] you cannot see my face: for there shall no man see me, and live" (Exodus 33:18–23). If all of God’s "goodness" were shown to a sinner, he would instantly die. God’s "goodness" would just spill wrath upon evil man.

However, the Lord told Moses, "It shall come to pass, while my glory passes by, that I will put you in a cleft of the rock, and will cover you with My hand while I pass by." The only way a sinner can live in the presence of a holy God is to be hidden in the Rock of Jesus Christ (1 Corinthians 10:4). Besides, God has made himself very clear through the creation of the universe. When you look at a building you see the work of a builder, when you see a painting you know there is a painter, so also when you see creation you know there is a creator.

FOR MORE INFORMATION:
http://www.gotquestions.org/Does-God-exist.html