We know God's Truth through Conscience
God leads us to discover his truth, not only through creation, but also through our conscience - Some things are hard wired in us by God; we know they are always right or always wrong, no matter what anybody else says. Our conscience tells us this. Say we take a random sample of one million people from around the planet and put them on a corner in New York City. We say: "Here's a 92-year-old blind lady with a walker. She needs to cross the street. Tell me which of these three options is morally right. One, you can let her try to cross on her own. Two, you can help her cross the street. Three, you can push her into on-coming traffic." You don't have to be a Christian or Jew or Muslim or even a spiritual person; inside you know the right thing to do. The Bible says, "Even Gentiles, who do not have God's written law, show that they know his law when they instinctively obey it, even without having heard it. They demonstrate that God's law is written in their hearts, for their own conscience and thoughts either accuse them or tell them they are doing right.
“for when Gentiles, who do not have the law, by nature do the things in the law, these, although not having the law, are a law to themselves, who show the work of the law written in their hearts, their conscience also bearing witness, and between themselves their thoughts accusing or else excusing them)”
Romans 2:14-15 NKJV