The heavens are telling of the glory of God; And their expanse is declaring the work of His hands.
Day to day pours forth speech, And night to night reveals knowledge.
There is no speech, nor are there words; Their voice is not heard.
Their line has gone out through all the earth, And their utterances to the end of the world. In them He has placed a tent for the sun,
Psalm 19: 1-4
They are a constant testimony to God and his power, who he is. Romans 1 says non-believers will have no excuse of being ignorant of God, because creation itself points to the creator. God has communicated to mankind both verbally & non-verbally.