The three essentials

Shaykh Ahmad Ali Lahori (Allah have mercy on him) said,

‘The spiritual benefit (from a Sahykh) is received via having reverence (aqidet) for him, observing proper etiquette (adab) with him and following his instructions (thoroughly).

Even if a single wire of this (three wire-cable) is broken the circuit breaks (hence, no benefit is achieved). 

Mard-e-momin, page 208