Idiom meaning "If it should be (x), it would be (x)"?

Is there some kind of saying or idiom in English with the meaning

if it were supposed to be like that, it would be (like that)

Something like

if it should be, it would be

Perhaps "it wasn't meant to be" would suffice. It can convey acceptance or an (often clumsy) attempt at reassurance. "Oh well, I guess it wasn't meant to be" is acceptance. "I'm sorry she said no when you asked her to marry you. It just wasn't meant to be" is a rather insensitive way of consoling someone.

There is a saying "If it were that easy, someone would have already done it." which captures some of the meaning in your original statement. It doesn't quite convey the same sense of things that are supposed to be, though.

Alternatively there's "It is what it is" which is a tautology, but kind of gets at the meaning your phrase hints at.

I think Alexander Pope said it best in his Essay on Man:

All nature is but art, unknown to thee
All chance, direction, which thou canst not see;
All discord, harmony not understood;
All partial evil, universal good:
And, spite of pride in erring reason’s spite,
One truth is clear, whatever is, is right.

(gutenberg)

It's expressing Leibniz's idea that this is the Best of all possible worlds

The claim that the actual world is the best of all possible worlds is the central argument in Leibniz's theodicy, or his attempt to solve the problem of evil.

Among his many philosophical interests and concerns, Leibniz took on this question of theodicy: If God is omnibenevolent, omnipotent and omniscient, how do we account for the suffering and injustice that exist in the world?

For Leibniz, an additional central concern is the matter of reconciling human freedom (indeed, God's own freedom) with the determinism inherent in his own theory of the universe. Leibniz' solution casts God as a kind of "optimizer" of the collection of all original possibilities: Since He is good and omnipotent, and since He chose this world out of all possibilities, this world must be good—in fact, this world is the best of all possible worlds.

On the one hand, this view might help us rationalize some of what we experience: Imagine that all the world is made of good and evil. The best possible world would have the most good and the least evil. Courage is better than no courage. It might be observed, then, that without evil to challenge us, there can be no courage. Since evil brings out the best aspects of humanity, evil is regarded as necessary. So in creating this world God made some evil to make the best of all possible worlds. On the other hand, the theory explains evil not by denying it or even rationalizing it—but simply by declaring it to be part of the optimum combination of elements that comprise the best possible Godly choice. Leibniz thus does not claim that the world is overall very good, but that because of the necessary interconnections of goods and evils, God, though omnipotent, could not improve it in one way without making it worse in some other way.

(wikipedia)

To bring in a religious aspect, the construct if God had meant for ... He would have .... For example, someone who hates aircraft might say "If God had meant for people to fly, he would have given us wings."