As for rabita, it is defined as tying one’s heart to the accomplished murshid and, in the process, keeping his image in one’s imagination, even in his absence, which is called tasawwur.
They said that the murshid is like a roof-duct: spiritual outpouring descends from his heart to that of the connecting (murabit) murid. In accordance with the hadith “Man is with whomever he loves,” the murid actualizes in himself the murshid’s features and states. Hence, al-Khani said in al-Bahjat al-Saniyya, self-extinction (fana’) in the shaykh is the prelude to self-extinction in Allah Most High. Imam Ahmad al-Sirhindi said: “It must be known that wayfaring in the Most Distinguished Way [Naqshbandiyya] is through the rabita and love for the shaykh being followed… his look is a cure for the diseases of the heart, and his tawajjuh lifts away spiritual ills.”
The Naqshbandi Masters, Allah be well-pleased with them, said that suhba or companionship is the foremost and strongest independent way of all to reach the Divine presence, followed in strength by rabita. This is what Shaykh Muhammad ibn Sulayman al-Baghdadi said in al-Hadiqat al-Nadiyya and, after him, Shaykh Muhammad ibn `Abd Allah al-Khani in al-Bahjat al-Saniyya.
The latter cited a passage of Imam al-Nabulusi’s commentary on Ibn al-Farid’s Khamriyya which brings together the benefits of suhba, tawajjuh, rabita, and tasawwur:
“Whatever meanings the wayfarer imagines of the manifestations of the Divine Presence during his presence with It, by the power of this divine Presence and not by himself, are but from the murshid through the latter’s tawajjuh (turning to Allah with the heart) and through supply from the Most Merciful (imdaad rahmaani). Sometimes this happens by the heart-to-heart’s inspirational address, with a truthful state. Sometimes it happens through explicit discourse or allusions. Sometimes it happens by giving the well-known cloak of the Sufis to wear. The pre-condition of all this is perfect truthfulness from both sides. Thus, the murshid’s truthful state, by the leave of Allah Most High, permeates the truthful mureed. Sometimes the truthful shaykh gazes out of the hadith qudsi ‘I become his eyesight by which he sees.’ Sometimes the murid looks to the shaykh out of the hadith ‘When they are seen, Allah is remembered.’ All this matter varies, speedwise, according to preparedness, sincerity in serving the shaykh, and manners with the shaykhs as well as safeguarding their honor both in their absence and in their presence.”
Among the vivid illustrations of the benefit of connection with an accomplished murshid is the following passage from Shaykh Hasan Hilmi al-Quhhi al-Daghistani’s Tanbih al-Salikin (p. 268):
“Whoever enters Tariqa and strives in worship becomes an enemy of shaytans and therefore needs a guard guarding him from them continuously. This is why the shaykh orders him to do rabita with an accomplished shaykh. If the shaytans were to approach the latter, they would almost be burnt by his light. The meaning of this protection is that it is a customary cause, just like medication or a weapon, and the effecter is Allah Most High. *He* is the all-encompassing Guardian and Watcher.”
May Allah Most High protect and grant you and us the acts and states He loves and may He bless and greet the arch-leader of Messengers and Prophets, his Family, and all his Companions.
Taken from: http://www.livingislam.org/k/ttsr_e.html