Purna Yoga means
(1) that instead of approaching the Divine through the mind alone (Jnana) or the heart alone (Bhakti) or through will and works alone (Karma Yoga), one seeks the Divine with all the parts and powers of the consciousness and the being, uniting these three ways and many others in a single Yoga (way of union with the Divine) and receives the Divine in His presence, consciousness, force, light and bliss in all the consciousness and the being.
(2) That one seeks not only the realisation of the Divine in the soul and self but also in the whole nature (that means the transformation of this lower human into the Divine spiritual nature).
(3) That one seeks the Divine not only beyond life (by the cessation of birth) but for life, so that life also may become a realisation of the Divine and a manifestation of the Divine Nature.
Ref: Letters on Yoga – II