How do we know God exists?

Human reason can know with certainty that God exists by reflecting on creation and the human person. God has also revealed Himself personally in salvation history, above all in Jesus Christ.

What reason can discover. The universe does not explain its own existence. Things within it come into being, change, depend on causes, and could have failed to exist. A complete explanation must reach a reality that does not receive existence from another, but exists necessarily and gives existence to everything else. Classical philosophy calls this reality the first cause or necessary being. The Church teaches that God's existence can be known from the created world by the natural light of human reason (CCC 31-35, 36; Rom 1:20).

Signs within creation. The order, intelligibility, and beauty of the universe point beyond blind contingency toward divine wisdom. Scientific explanations describe physical processes, but they do not answer why anything exists, why nature is intelligible, or why rational laws govern it. Faith and genuine science cannot contradict each other because both truth and creation come from God (CCC 159). The Church does not treat God as a temporary explanation for gaps in scientific knowledge. God is the reason there is a universe with causes and laws at all.

Signs within the human person. People naturally seek truth, goodness, justice, beauty, and lasting happiness. Conscience places us under a moral law that we recognize rather than invent. Human freedom, rationality, and openness to the infinite also point beyond matter alone (CCC 33). These considerations do not force belief like a mathematical equation. Together they form rationally compelling paths toward the one Creator, source of being, truth, and goodness.

Why revelation is still needed. Reason can know that God exists, but it cannot by itself discover the full mystery of the Trinity or God's plan of salvation. God freely revealed Himself to Abraham, Moses, Israel, and finally in His Son (CCC 50-53; Heb 1:1-2). Sin, distraction, suffering, and bad examples can make recognition of God difficult, so grace helps the mind receive the truth (CCC 37-38). If you are uncertain, begin honestly: ask God to reveal Himself, read one Gospel slowly, and examine the strongest arguments rather than popular caricatures.