Revelation, through creation

The creation bears witness to the wisdom and power of its creator. This natural knowledge of God is limited in its extent, but is sufficient to convince human beings of the existence of God and the need to respond to him.

The creation bears witness to its creator

Psalm 19:1–6 See also Job 36:22–37:18; Amos 4:13; Acts 14:15–17

For the choirmaster. A Psalm of David. The heavens declare the glory of God; the skies proclaim the work of His hands. Day after day they pour forth speech; night after night they reveal knowledge. Without speech or language, without a sound to be heard, their voice has gone out into all the earth, their words to the ends of the world. In the heavens He has pitched a tent for the sun. Like a bridegroom emerging from his chamber, like a champion rejoicing to run his course, it rises at one end of the heavens and runs its circuit to the other; nothing is deprived of its warmth.

All human beings have a natural awareness of God

Romans 2:14–15 See also Acts 17:22–31

Indeed, when Gentiles, who do not have the law, do by nature what the law requires, they are a law to themselves, even though they do not have the law. So they show that the work of the law is written on their hearts, their consciences also bearing witness, and their thoughts either accusing or defending them

The limitations of a natural knowledge of God

Romans 1:18–21 See also Romans 1:32; 1 Corinthians 1:20–21

The wrath of God is being revealed from heaven against all the godlessness and wickedness of men who suppress the truth by their wickedness. For what may be known about God is plain to them, because God has made it plain to them. For since the creation of the world God’s invisible qualities, His eternal power and divine nature, have been clearly seen, being understood from His workmanship, so that men are without excuse. For although they knew God, they neither glorified Him as God nor gave thanks to Him, but they became futile in their thinking and darkened in their foolish hearts.