Q. 2. How doth it appear that there is a God?
A. The very light of nature in man, and the works of God, declare plainly that there is a God; but his word and Spirit only do sufficiently and effectually reveal him unto men for their salvation.
 Romans 1:19-20. Because that which may be known of God is manifest in them; for God hath showed it unto them. For the invisible things of him from the creation of the world are clearly seen, being understood by the things that are made, even his eternal power and Godhead; so that they are without excuse. Psalm 19:1-3. The heavens declare the glory of God; and the firmament showeth his handiwork. Day unto day uttereth speech, and night unto night showeth knowledge. There is no speech nor language, where their voice is not heard. Acts 17:28. For in him we live, and move, and have our being; as certain also of your own poets have said, For we are also his offspring.
 1 Corinthians 2:9-10. But as it is written, Eye hath not seen, nor ear heard, neither have entered into the heart of man, the things which God hath prepared for them that love him. But God hath revealed them unto us by his Spirit: for the Spirit searcheth all things, yea, the deep things of God. 2 Timothy 3:15-17. And that from a child thou hast known the holy scriptures, which are able to make thee wise unto salvation through faith which is in Christ Jesus. All scripture is given by inspiration of God, and is profitable for doctrine, for reproof, for correction, for instruction in righteousness: That the man of God may be perfect, thoroughly furnished unto all good works. Isaiah 59:21. As for me, this is my covenant with them, saith the LORD; My spirit that is upon thee, and my words which I have put in thy mouth, shall not depart out of thy mouth, nor out of the mouth of thy seed, nor out of the mouth of thy seed's seed, saith the LORD, from henceforth and for ever.
-Taken from the Westminster Larger Catechism