It always means that you must sacrifice something very dear to you when His call comes.
When we think deeply about the problem of life, there is no path in the world, whether spiritual or material, which we can tread successfully without a sacrifice. Sometimes the sacrifice is great, and sometimes small; sometimes the sacrifice is made first, before achieving success, and sometimes afterwards. As sacrifice is necessary in life, it is made by everyone in some form or other, but when it is made willingly, it turns into a virtue. The greater the ideal, the greater the sacrifice it demands… sacrifice of a possession is the first step; the next one is self-sacrifice, which was the inner note of the religion of Jesus Christ. Charity, generosity, even tolerance and forbearance, are a kind of sacrifice, and every sacrifice in life, in whatever form, means a step towards the goal of every soul.
from http://wahiduddin.
I gave up my music because I had received from it all that I had to receive. To serve God one must sacrifice what is dearest to one; and so I sacrificed my music. I had composed songs; I sang and played the vina; and practicing this music I arrived at a stage where I touched the Music of the Spheres. Then every soul became for me a musical note, and all life became music. Inspired by it I spoke to the people, and those who were attracted by my words listened to them, instead of listening to my songs.
Now, if I do anything, it is to tune souls instead of instruments; to harmonize people instead of notes. If there is anything in my philosophy, it is the law of harmony: that one must put oneself in harmony with oneself and with others. I have found in every word a certain musical value, a melody in every thought, harmony in every feeling; and I have tried to interpret the same thing, with clear and simple words, to those who used to listen to my music. I played the vina until my heart turned into this very instrument; then I offered this instrument to the divine Musician, the only musician existing. Since then I have become His flute; and when He chooses, He plays His music. The people give me credit for this music, which in reality is not due to me but to the Musician who plays on His own instrument.
~ Hazrat Inayat Khan
from http://wahiduddin.
Another Sufi example of sacrifice occurs with Shams-i Tabrizi's disappearance from Konya, Turkey after having taught Jallal al Din'l Rumi for three years. Some versions of this story say that one of Rumi's sons, jealous at the way Shams and Rumi got along together, murdered Shams late at night in the street. Some who report this version of the story also maintain that no such individual ever actually existed and that he was a literary tool used by Rumi in his writings.
There had already been one earlier occurrence of Shams' leaving Rumi behind and going to Damascus, but he was known to have returned to Konya from Damascus. Rumi's student were always around when the two of them got together, taking notes and writing down the stories shared back and forth, and it is from these notes that much of this history is recorded.
At one point Shams saw it a necessary step to leave Rumi behind once and for all, this being the incident that made Rumi develop into writing his greatest works of poetry and spurring him forward in the spiritual sense, into his own state of Mastery. Shams at this time went onward to Khoy where he continued teaching others, writing his lessons down and living to a ripe old age which is referenced in his writings. This is the proof that this version of that story is closer to the actual events concerned.
The point being that Rumi was forced to sacrifice his friendship, and the pain he felt at this parting was exactly what spurred his consciousness forward into ever more complete states of awareness and inner experience. The sacrifice was the cost of those lessons, and as such had to be paid.
The ability to sacrifice, and to avoid being overly attached to the mental and emotional states that always arise during such incidences, not only frees the true self, but spurs it into further action and ascending the states of consciousness and being until ever newer regions are experienced and are made to be the constant living states of such beings. Talk is cheap, but actual experiences are anything but, and often come because of the high price that must be paid to attain these states. Patience and perseverance are always the tools that must be kept on hand, as these make the successes possible.