OP, why is the sky blue and not green? Why do cats have four paws instead of five?
Answer: Because that's the way God wanted it to be.
Well, yes, that is how things are because that's how God designed things to be. But it's not just some "God done it" answer. There are actual answers to those questions.
The sky is blue rather than green because of the sun's light spectra, Rayleigh scattering, and the composition of our atmosphere. Under different circumstances a green atmosphere would be possible, for example a chlorine-rich atmosphere would probably be enough to turn a planet's sky green.
And the reason cats have four paws and not five is because cats are tetrapods. Given the bilateral symmetry of all bilaterian organisms, any bilateral organism that has limbs is going to have an equal number of limbs on either side. Which is why we see bilaterian organisms with four, six, eight, ten, etc limbs. Obviously a five-limbed organism is possible, many sea stars--which have radial symmetry like all other echinoderms--can have a highly diverse limb (or protrusions of some kind) arrangement around the center body. So cats have four paws because they are tetrapods, and all members of tetrapoda are also members of bilateria.
It's probably a good idea to both offer the known explanation for these things while also giving God honor as the One who made all things. With all due respect, the alternative seems to discourage rational thought and genuine inquiry--which are good things.
Now when it comes to certain matters of faith, our reason and the use of the rational does not necessarily get us from point A to point B; and that's okay. But when there definitely are answers, or where answers are possible, they should be sought out, and we should use rational and critical thinking in those endeavors.
In the Mystery of the Cross, there are good answers to the question, even if there may be aspects of the Mystery which are beyond us at present. Christ's death is a very deliberate act of God, God the Son very deliberately chose to suffer, chose to become flesh and be crucified--it wasn't "just because", it was because through this God becomes a participant with us in our humanity--that means death--and through this makes us participants with Him.
Or as St. Athanasius wrote, "God became man in order that man might become god." Which if you're not familiar with the historic doctrine of Theosis this might sound shocking, but it's simply what St. Peter himself says in his epistle, that we have become partakers of the Divine nature. Christ our God has shared in our humanity, and by our union to Christ we share in His Divinity. We aren't divine, and will of course never be divine--but in Christ we share in the life of God who is Divine.
-CryptoLutheran