The richest and most beautiful of all the so-called proofs for the existence of God is the teleological (design & purpose). It means to lead us up not only to a superpower over all, or final cause of the world, but also to a personal designer of all things, possessed of intellect and will, of knowledge and wisdom.
In the world about us, as well as in our own being, we see design and purpose everywhere. How beautifully and perfectly all things are adapted to one another so that each creature exists, moves, lives, and acts within the sphere of its own law, and all its needs are satisfied. The fish is adapted to the water, the bird to fly in the air, the beast to roam in the jungle, trees and flowers to grow and flourish in the soil, and clouds, rain, and sunshine to cause the seed to sprout in the earth. The eye is adapted to the light, the ear to sound. The human mind is adapted to interpret the world round about it and to subject all things under it.
Everywhere there is purpose and design, and all things loudly proclaim a designer marvellous in wisdom, goodness, and power. That designer is God. To be sure, the believer loves this argument. He loves to sing with the inspired Psalmist: “O LORD, how manifold are thy works! in wisdom hast thou made them all: the earth is full of thy riches” (Psalm 104:24). Again this is the language of faith, not of reason without faith, and it is based on Revelation (Bible). Faith does not seek to prove the existence of God, but proceeds from the certainty of existence.
As far as pure or unbelieving reason is concerned, let us note that also this so-called proof proves exactly nothing as to the existence of an intelligent being outside of the world, who is infinite in power and wisdom and the designer of all things. It may as well be employed by pantheistic evolutionism to demonstrate that nature itself is intelligent, that God is the world, and the world is God, reaching his highest consciousness in man.
Moreover, if there is design in the universe, there are also many phenomena that would seem to demonstrate the very opposite of design and purpose. There is friction, conflict, death, destruction, and apparent foolishness everywhere. A babe is born, and its mother dies in the pangs of birth, or the babe itself is snatched away by the merciless hand of death. A tree grows, and the lightning strikes it down. A crop is almost ready for harvest, and a hailstorm destroys it. The world as we perceive and know it today is full of phenomena that appear to be foolish, that some have denied the design altogether and have pronounced the universe the worst that anyone could possibly have conceived.
Faith is God’s revelation (Bible) has its answer to these objections, for it knows of God’s wrath against sin, and it considers the wisdom of God in the face of Jesus Christ the Lord, in whom the believer finds the solution for all of these phenomena and looks in expectation for the final and perfect theodicy (vindication of divine providence in view of the existence of evil) in the day of the revelation of the righteous judgment of God. But unbelieving reason that sets aside or contradicts God’s own revelation (Bible) of himself cannot recover God in the way of the teleological (design & purpose) argument. As a rational proof it has no power.
(Reformed Dogmatics, H. Hoeksema)