This is the post #6 of the Calvin's Institutes summary series.
Since the nature is not sufficient to make people to know God truly, although it is enough to condemn all people for rejecting God, God has given us His Word so we may truly know Him. We can know God as Creator and as Redeemer. For one to be saved, one must know God as both Creator and also as Redeemer. God's own Word is necessary for knowing God as Creator, not just for knowing Him as Redeemer. Our minds are so weak and corrupted, we always conjure up false gods when we look at the creation, even though it's singing God's praise every second. God has given His own Word to reveal Himself, and had it written for the our security. Without this Word of God, people will continually fall into error, and we must come to the Word again and again, since we are so forgetful (and sinful). Conclusion: while the creation declares the glory of God, we must come to the Word in order to gain true and sure knowledge of God.
My note: It seems Calvin is labouring in these sections so far to establish the point that knowing God as Creator cannot come about by simply contemplating on nature (empiricism?) or by reason alone (rationalism?). He might be doing this in order to counter the claim that says the Scripture is only needed to know God as Redeemer, but God the Creator can be known from the nature or reason alone. Maybe this view was a prevalent one in the Roman Catholic church in Calvin's day.