A lot of people have wondered about that very question. AND a good number of people have written very good guidance for answering it.
- When God speaks, you usually don't have to worry about whether or not it was God. You just know. God's voice quite often leaves an impression. If you don't just know, then be skeptical.
- At the same time, Scripture encourages us to "test the spirits" to see if they are really of God. Here are some good tests:
- Have you resigned your will completely so that you are ready to hear whatever God would say to you? If you haven't, you will confuse yourself. For example, if you are buying a car, and you really want this particular car, and you can afford it, and everything seems good, but then you pray and you hear, "Don't buy that car," you will find yourself thinking, "Was that really God? Surely not." You have to FIRST let go all preconceived ideas and listen from that place of openness that is resigned to God's will BEFORE you start putting together your own thoughts about it, or else you can get really confused.
- Is it consistent with Scripture? God NEVER says anything contrary to what he says in Scripture. A young man once began sleeping with his girlfriend, and when confronted about it by his youth pastor, he said, "Well, I prayed about it, and I have peace that this is okay with God." That peace wasn't from God, and had he been willing to hear God's "No," clearly stated in Scripture, it was there for him. Also, Scripture points us to the church to guide and protect us, and those people (his Christian friends, parents, his youth pastor) were telling him that he was wrong. In every way, Scripture itself disclaimed his "peace."
- Does it produce good fruit? Scripture says that the word of God is a "double-edged sword, able to divide joint from marrow." When you hear his word, and when you repeat it to yourself and others, it has great power. For example, one day at a worship service, a man was praying, and he suddenly heard God speak his name to him. It was not just some odd hearing of the syllables of his name. It carried such great power that he spent the rest of his life drawn to the God who spoke his name at that moment. The word led to worship, obedience, and a life of godly love, joy, and peace.
Of course, God also speaks through circumstances and people. And saturating our mind with Scripture IS saturating our minds with God's word, by which we will often just know exactly what God would want us to do in any given situation. However, Christians throughout all centuries will attest that God does speak directly to his people, too. Since no one keeps on talking to someone who won't listen, let's all make sure we are open.