On observations, and empirical evidences

Fine-tuning is an extraordinary balancing of the parameters of physics, at both the sub-atomic level, and across the expanse of the measured universe. It is perhaps, one of the strongest examples of evidence for Theism, over an Atheistic single universe hypothesis, as fine-tuning bares witness of the required parameters, for intelligent life to exist.
 
Through observation and empirical evidence, we witness solely, a single universe. Therefore, if we were to treat a Theistic single universe hypothesis (H1) as competing with an Atheistic single universe hypothesis (H2), we could draw upon the methodology commonly used in science for making an inference to the best explanation. This being, how well do the predictions of the model match the observation? A Theistic model predicts a universe created using intelligent design, with care and consideration for its creation (H1). An Atheistic model, considers that the constants governing the laws of physics were either set randomly, or without necessary respect for intelligent life to evolve (H2).
 
Probabilistic reasoning supports the notion that fine-tuning is the result of an intelligent mind, and that fine-tuning is not improbable under Theism, while fine-tuning in an Atheistic single universe hypothesis is highly improbable. The Epistemic Probability, or the measure of the rational belief we should have in a preposition, such as Intelligent Design, or Blind Force, also favours H1.
 
Some hold to a single but periodically reforming universe hypothesis (H3), however, we have nothing but speculation to forward this notion. This holds true, also for the multiverse hypothesis (H4). There exists no scientific evidence for the existence of this multiverse, nor can it be physically detected, observed, measured or proved, and all we do by forwarding these notions is to increase the level of fine-tuning to an abstract 'universe generator'.
 
If we consider the probability calculus, and recognise that there is no good reasoning that violates the principle of H1, we find an intelligent designer appears to be the only plausible explanation for the existence of order and structure in our universe. This is a logical, rational deduction based upon our own human experiences, having intelligent minds with an ability to create, and from recognizing a fundamental law of biology; life comes from life.

And while fine-tuning is not definitive proof of 'God', it does provide substantial evidence for His existence, and may reveal purpose in creation, and the choice of laws of science.

Fine tuning. A fine argument for Theism.