When it comes to any religion, this is one of the first questions to pop up in one's head and is definitely the hardest ones to answer as well. Based on how each religion handles the question, the entire philosophy of that religion is constructed. Before we start answering the question, let us first see the definition of God.
According to Merrian-Webster dictionary [*], the primary definition of God is as follows:
The supreme or ultimate reality: such as the Being perfect in power, wisdom, and goodness who is worshipped as creator and ruler of the universe.
According to Wikipedia [*], which is also in-line with our common understanding, (monotheistic) God is conceived of as the supreme being, creator deity, and principal object of faith. Also, God is conceived as being omniscient (all-knowing), omnipotent (all-powerful), omnipresent (all-present) and as having an eternal and necessary existence.
Now, let us attempt to answer this question step by step and see where it takes us.
Step 1 - A Creator:
Let us consider an example. Suppose an observer sees a lump of clay in a corner. After a while, the observer notices a pot in the same place. The observer can quite evidently infer that the clay has transformed into the pot and that everything that constitutes the pot is actually the clay. But, the pot has a defined shape and texture and is not a random lump like the clay. In other words, there is an order associated with the dimensions and other attributes of the pot. Also, by the design of it, the pot seems to also have a purpose, i.e., to contain water, curd, and such.
Now, both the clay and the pot are inert objects. Is it possible for an inert object to transform itself into another, let alone having defined attributes? If it could, then it contradicts the definition of inertness. Thus, there must be an influence that has caused the clay to transform into the pot. From this, it is evident that any object that has order or purpose could not have been created without conscious intelligence.
Using the analogy to this universe, it is not very difficult to understand that there must be an intelligent Creator that has caused this universe to exist and orchestrates it the way it does. Quite evidently, this intelligence cannot lie outside the universe to influence, for nothing lies outside of it. Whoever has caused this creation is part and parcel of the universe.
Modern science acknowledges that everything started from a single dense point a.k.a singularity [*]. It is not clear whether there was any meaning to matter, space or even time at this point. This is mind-boggling to even the greatest scientists as to how something with such an order can just pop out of a massively dense object but yet not collapse as it is supposed to according to the law of physics as we understand it today. The laws that govern the universe are devised in such a way that even the slightest alteration to these would crumble the existence of it. This creation is just in perfect balance with both order and purpose which is only possible by a conscious intelligent Being!
This clearly fits the above description of God, who has created everything, framing rules to the minutest detail. One way or the other, this is what every monotheistic religion in the world calls God from the creation perspective.
Step 2: So, there is a Creator who framed the laws of physics, alright. But, what do we care? In other words, why should we pray to the Creator?
This is a much trickier question than the earlier one. Let us elaborate on the question further. If God is as per the definition, omnipotent, omnipresent, and omniscient, then surely He/She should not need our prayers to get flattered. Also, it surely is not wholesome to know one's problems but wait until a prayer to fulfil their wish. In fact, God created both us and the problems we face. So, it surely is His/Her responsibility to solve them for us too! Finally, we know that every action has a consequence and that, things go according to rules. Subsequently one may think, of what use is it to pray to God if things are already fixed.
Instead of trying to prove whether God can alter destiny, or bend the rules, let us focus on what prayers can fetch.
Let us keep in mind that God is free of all desires as there is nothing for Him/Her to achieve. People pray to God to let Him/Her know of their problems, place a wish, or occasionally thank as a matter of courtesy on account of a fulfilled wish. It is not that God gains anything by this prayer. It violates the definition of God otherwise. Does that mean prayers are of no use? Not necessarily. By praying, one submits their ego to a Higher Being, far superior to any other, and momentarily feels humility, letting go of all the false pride.
Emotions such as anger, hatred, sadness, fear, joy, lust are all due to desires that arise in the mind. Any action that one does has a consequence which affects the mind in one or many ways. A source that causes pleasure now may cause pain at a later point and vice versa. Also, these emotions don't last forever either. Unless one puts the mind to rest, one cannot be free from this emotional turmoil and never be at peace. Slowly, by submitting oneself to God, one gains serenity, and ultimately subdue desires, yet performing actions. Once one becomes desireless, there is nothing more to achieve akin to the state of God. This is eternal bliss!
Thus every act of prayer or Bhakti to God by complete surrender takes us a step closer to know one's real Self which is the desireless state of eternal bliss.
References:
Deivathin kural (Voice of God) Volume 1, Compiled by R.Ganapathy, Vanathi Pathippakam
Deivathin kural (Voice of God) Volume 3, Compiled by R.Ganapathy, Vanathi Pathippakam
