God is present everywhere for His all-pervasiveness is His nature. ‘Logically’ one can, therefore, meditate on Him wherever one wants to meditate on. But in pure heart, free from all negative ideas such as lust, greed, jealousy, anger and so on, God is manifest more.
Sri Ramakrishna used to call heart as ‘the drawing room’. In a house, the master of the house can move around, and hence can be found, in any part of the house. But most likely, the master can be found in his drawing room. That is where he is most comfortable and relaxed. Likewise, while God can be meditated anywhere, He is most visibly present in the pure heart of a devotee.
Lotus is also a symbol of devotion. While meditating on God, one is asked to meditate on a bloomed lotus in the centre of chest. Like a lotus, a pure heart never gets dirty by the mire called worldly thoughts and negative emotions. It is ever pure, and fresh, and a fitting place to think of the Presence of God.
Sri Ramakrishna says: It is one thing to know that there is
fire in the wood and quite another to generate it by friction between two
pieces of wood. It is one thing to know that milk is good for health but quite
a different matter to drink and be benefited by it. Likewise it is one thing to
know that we are all divine but quite another thing to realize it, experience
it. We know ourselves mostly as fair or dark, of a certain height, weight and so
on. What does this all denote but the body? The body is only a vehicle for the
Self to work through. It is only a structure. As the temple is no temple as
long as there is no image of God installed within it, so too, so long as God is
not realized within, the body is only a collection of bones, flesh and so on.
Source – The Vedanta Kesari September 2010 Edition