It should be noted, firstly, that the concept of Emptiness (shunyata) does not exist in the Theravada tradition of Buddhism. It is a Mahayana Buddhist term. The term closest to Emptiness in Theravada Buddhism is Non-self (anatman). So why these separate terms?
In Theravada Buddhism the Buddha’s teaching of Non-self is interpreted to mean only no essence of the self, the sentient being. Mahayana Buddhism interprets Non-self to mean all things, animate as well as inanimate. This is why Mahayana Buddhists to distance themselves from the term No-self by taking a word to cover the wider definition they believed the teaching of Non-self to mean.
This is why Form and Emptiness are spoken within the same breath in the Heart Sutra. Whether one accepts the Theravada or Mahayana is up to the individual. What is important is to know at least this difference exists in Buddhism. It is a matter of interpretation.
This ‘no’ is not the no in the phrase ‘I have no money’. Whether one has money or not is not of importance. The ‘no’ is rather like the ‘-less’ in ‘priceless’ meaning ‘beyond a value’ where it is not attached to existence or non-existence.
And what is the ‘form’ of ‘no form’? It the very way our physical body works. The heart pumps. The blood flows. Rhythm follows. We breathe. We grow. And we change. But to go beyond this understanding of good and bad is the meaning of the phrase ‘no form’.
It is this life, this reality, without principles, without discrimination that we have simply overlooked.
We should be attentive to the ‘no form’ which is without attachment in all its working.
(My translation of Choyaku Hannya Shingyo, pp88-9, by Sakaino Katsunori, ISBN 9784837981619)