I WAS AMUSED TO SEE THIS BILLBOARD, just around the street-corner. It showed a hip-looking youth dressed in the latest designer wear. And this was his motto in life. What does it mean? 
'I am God', or 
'I do not need any other God in my life', or 
'You too can be your own God'. 
Generally, in Our honest moments one may acknowledge ignorance of a particular subject, but surprisingly, I have rarely met someone who honestly admits, "I actually do not know who God is, but would like some help in this matter." 
Here is some help anyway. 
Theistic traditions in India had two main streams – The monists or those who maintained that God is in the ultimate sense an 'impersonal force', and the Vaisnavas (devotees of the Supreme Lord Visnu) who wanted to serve a personal God eternally. Apart from these two are the Mayavadis, who maintain that everything (even God) in the ultimate sense is illusion or ignorance. 
Let us begin with adefinition of ourselves – Who are we? How do we size up? A definition from the Upanisads states – When the tip of a hair is divided into one hundred parts and again each such part is further divided into one hundred parts, then the size of the final part is the measurement of the dimension of the spirit soul. 
Another similar one goes – 
"'There are innumerable particles of spiritual atoms, which are measured as one ten-thousandth of the upper portion of the hair." 
And now here is a definition of God – He is a person, full of all wealth, strength, fame, beauty, knowledge, and renunciation – these are the six opulences of the Supreme Personality of Godhead. Arjuna acknowledges in the Bhagavad-gita that – O Krsna ,You are the Supreme Personality of Godhead, the ultimate abode, the purest, the Absolute Truth. You are the eternal, transcendental, original person, the unborn, and the greatest . … O Krsna, 1 totally accept as truth all that You have told me. Neither the demigods nor the demons, 0 Lord, can understand Your personality. (B.g. 10. 12-13) 
So there it is. The difference between us and God exists. We are infinitesimal while He is infinite. Then what about those who want to merge in Him? 
The monists in India are very fond of the example of the rivers merging in the ocean. After the waters of a river join the ocean there no longer remains a distinction between the river-water and the ocean-water. Similarly, the monists contend, once we achieve liberation, then what is the difference between us and God? – We become ONE. This is indeed glorious, if it was really like that! A small problem with this analogy is that what about evaporation of water. The rivers have indeed merged and all the water molecules are blissful in their 'liberated' state, but then due to the summer sun as water gets evaporated, does such thing happens to these 'liberated souls'. Indeed it happens, according to the Srimad-bhagavatam: 
[Someone may say that aside from devotees, who always seek shelter at the Lord's lotus feet, there are those who are not devotees but who have accepted different processes for attaining salvation. What happens to them? In answer to this question, Lord Brahma and the other demigods said:] O lotus-eyed Lord, although nondevotees who accept severe austerities and penances to achieve the highest position may think themselves liberated, their intelligence is impure. They fall down from their position of imagined superiority because they have no regard for Your lotus feet. (SB 10.2.32) 
The Srimad-Bhagavatam narrates the history of the four Kumaras (Sanak, Sanatana, Sanandan, and Sanat-kumara) who were monists but were attracted to the personality of God later. These wandering saints happened to smell the fragrance of the tulasi-leaves offered at the lotus-feet of Lord Visnu and that caused a great change in their hearts. Thus they became great bhaktas or devotees of Lord Visnu. 
We can see a green parrot streak across the sky and perch on the branch of a tree. Well, since we cannot exactly trace out the parrot we can very well imagine that he has merged. But that has not happened. Look closer and you will find that he has kept his individual identity. Similarly there is no merger possible, except one where God and the living entity have one common interest. 
 (Syamananda Dasa)