What is the difference between a Zahid, an Aabid and an Aarif, according to Ibn Sina?

In his famous book Kitab al-Isharat wa al-Tanbihat, Ibn Sina distinguishes the Zahid, the Aabid and the Aarif, and it is the Aarif he holds worthy of the title of Sufi and of being venerated as the vicegerent of Allah. He explains:

"The man who is devoted to absolute abstinence of worldly pleasures is called 'Zahid' and the man who keeps almost every moment of his life devoted to worship is called 'Aabid'. The man who keeps his attention perennially focussed towards Qudoos-e-Jabroot (The Holy Omnipotent) and expects every moment the Manifestation of Divine Light in his inner self to illuminate every spectrum of his life as a whole, is recognised and adored with the ever-shining title of 'Aarif'. In the opinion of Ibne Sina such an exceptional human amongst the countless creatures of Allah is worthy of being honoured by the title of Sufi and venerated as the vicegerent of Allah." [Ibn Sina, al-Isharat wa al-Tanbihat, vol. 4]