Due to self-study connection with one’s chosen deity.
The current evolution of human beings is in the form of homo sapiens meaning man of knowledge. Due to our brain development, we have the capacity to understand life, ourselves, the universe. Knowledge in fact has neither beginning nor end.
The highest knowledge is to know and understand man’s proper relationship with himself, the universe and the Divine. This is the essence of the knowledge contained in the Vedas (meaning book of knowledge).
One can better relate to and therefore better appreciate principles if they are made objective. This is the purpose of having an Ishta Devata or chosen deity as an embodiment of certain universal principles (e.g. Krishna as Love and Bliss, Rama as Dharma, Hanuman as Strength and Devotion, Kali as Universal Power, Shiva as Consciousness….). So we study and learn about the deity, are initiated into and practice its Mantra, and we do Puja and meditate on the deity slowly transforming our psyche into that of the deity.
This is a way to consciously (re)connect with the Self Within by connecting with a principle (one’s chosen deity) that is in essence unbound by the ego-self (limited by the physical self and a mind that is fixated either in the past or future). All deities (Cosmic Principles) are both within the individual and collective psyche, and are universally displayed for those who have the in-sight.
There is a Tantric dictum that states that Shiva (Consciousness) without Shakti (Power / Dynamism) is Shava or a corpse. This implies the ever-conscious expansion of our awareness in order to go beyond our current limitations in our understanding of who we are, of what the universe is and what our Higher Purpose is.
There is also another dictum that states that Shiva (Consciousness) is the greatest devotee of Krishna (Love, Sweetness and Bliss). This in turn implies that the most sublime purpose we can hold is to expand our awareness of others with profound interest in order to serve them with love.