Let me ask you a question: Even if you heard a voice claiming to be God, how would you know it actually was Him? How would you know your mind wasn't playing tricks, or that someone wasn't simply fooling you with a hidden speaker? The answer is, you probably wouldn't.
But listen: God does speak to us today, not in an audible voice, but in written words -- the words of the Bible. The Bible is God's Word, given to us so we can know Him and discover how He wants us to live. He also gave it to us so we can have hope -- hope of God's forgiveness, and hope for His presence with us, both now and forever. The Bible's words are true: "Every word of God is flawless; he is a shield to those who take refuge in him" (Proverbs 30:5).
Most of all, the Bible points us to Jesus Christ, who came from Heaven to demonstrate God's love for us. He did this by living a life of compassion and perfection -- and He did it most of all by giving His life as the perfect and final sacrifice for our sins. We know this is true, because He did something no one else could do: He rose from the dead, by the power of God.
Make the Bible part of your life, asking God to speak to you through its pages. Then respond to His Word by giving your life to Christ. When you do, doubts will flee and faith will prosper.