Nandi is lord Shiva’s vehicle
Generally We see him sitting directly opposite the main door of temple where Shiva's idol or Shivalingam is located.
He is not waiting for him to come out and say something.
He is in waiting.
Nandi is a symbolism of eternal waiting, because waiting is considered the greatest virtue in Indian culture.
One who knows how to simply sit and wait is naturally meditative.
He is not expecting anything. He will wait forever.
Nandi is Shiva’s closest accomplice because he is the essence of receptivity.
Before you go into a temple, you must have the quality of Nandi - to simply sit.
So, just by sitting here, he is telling you, “When you go in, don’t do your fanciful things.
Don’t ask for this or that. Just go and sit like me."
The fundamental difference between Prayer & Meditation is that - Prayer means you are trying to talk to God. Meditation means you are willing to listen to God.
You are willing to just listen to existence, to the ultimate nature of creation.
You have nothing to say, you simply listen.
That is the quality of Nandi – he just sits, alert, not sleepy. He is not sitting in a passive way, very active, full of alertness, full of life, but just sitting – that is Meditation.