1) The sermon of creation is not a minimal thing - it's maximal. Romans 1:19 'what may be known about God... God has made plain.' Colossians 1:23 'the gospel... has been proclaimed to every creature under heaven.' Psalm 19:2 'Day after day they pour forth speech.'
2) Our blindness/deafness to this sermon is not minimal either - it is maximal. Note that in Psalm 19 David trusts that the creation daily pours forth speech in intentional evangelism. In Ecclesiastes 1 his son sees the exact same heavens. Yet even with all his wisdom, the 'teacher' of Ecclesiastes finds it utterly meaningless. The circuit of the sun which was such a vivid portrait of the Bridegroom Champion in Psalm 19 becomes, in the eyes of the 'teacher', a futile and meaningless cycle.
Humanity is blind to the things of God (2 Cor 4:4; Col 1:21). We cannot judge what the sermon of creation is saying by what we see. We naturally only see what we want to see.
3) The sermon of creation is not a static thing, it's dynamic, it's about movement and action and inter-relation. Literally Ps 19:2 says "Day unto day is a pouring forth of speech; night unto night is a displaying of knowledge." The sequence of day and night and day and night is itself a display of knowledge. This proclamation involes 'sun, moon and stars in their courses above.' The sermon of creation is expressed in dynamic action, it does not simply speak to us in static snap-shots of beauty.
So often people simply characterise the sermon of creation as something like "Look at a snow-capped mountain range, doesn't it fill you with awe. Well, now you should direct that awe to the God who is big enough and clever enough to have made it." That is certainly an element to what creation is saying, but it's not what David is drawing our attention to.
Psalm 19 highlights the progression of day and night, the movement of the sun across the sky, the heavens in their courses. The dynamic sermon of creation tells far better of the Glory of God who is not a static, unmoved deity simply waiting for people to give Him glory. The Living God acts and moves and relates. And His Glory, according to the Bible, is His Son acting, moving and relating. The theist will think of the sermon of creation in static terms because her god is static. The Christian knows the sermon is dynamic - just like our God.
4) The sermon of creation is 'the word of Christ.' It is not about abstract qualities of power or wisdom but about the Son. Of course this is so since Jesus is eternally the image of God (Col 1:15). There is no revelation that is not in Him.
In Romans 10 Paul asks if any have not heard the word of Christ (v17)? He answers, of course not and quotes Psalm 19! The sermon of creation is the word of Christ. When we examine Psalm 19 we see this to be so. His example of the sun is a dead giveaway. This sun is like a Bridegroom Champion who moves from east to west (like the journey the high priest makes from altar to ark) as the light of the world. (Ps 19:4-6; cf Ps 45). Here is a sermon regarding Christ.
Think also of John 12. When Jesus picks up a seed He doesn't say "How pretty and how intelligently designed" - He says "This seed proclaims my death and resurrection and, though this, the life of the world." The sermon of creation is a gospel word concerning Christ.
5) Finally, the sermon of creation is seen only through the spectacles of the Scriptures (Calvin's famous image). Ps 19 continues 'The law of the LORD is perfect, reviving/converting the soul.' (v7) That which left even Ecclesiastes' 'teacher' looking into the meaningless cycle of life and death is that which, through the spectacles of Scripture, becomes the dynamic proclamation of Christ and His gospel.