nagpapatunay and yun

Hi,

Please help me in understanding this:

''Laging tandaan, pag nag judge sayo ang ibang tao. di yun nagdedefine kung siyo ka, pero yun ang nagpapatunay kung ano sila.''

Does it mean: ''People who judge others actually defines themselves"

What is the significance of the word 'yun'?

Regards,
Reflections