Siri Singh Sahib tells a legend of humanity:
In certain cases even our roots are shaken. We didn't know what to do. We went to the wise people. We went to the pandits. We went to the mullahs. We followed their advice yet still it got harder and harder. The wind of the time and the pressure of the space is so much.
Sometime the heavens become indifferent. Not cruel. And earth doesn't hold the balance. And our roots sometimes dry up, sometimes they are not together... We wanted something...
Entire humanity prayed.... and God descended... and came Nanak.
Out of his love he gave us the mool mantra.
He said when roots are shaken, they will replenish themselves, don't worry. I have come to serve thee as thee.
And thus humanity started chanting the root mantra. Mool mantra. Not only their roots became deeper, they became prosperous. They became courageous, they became angelic, they became free, they became divine, they became godly, they became priestly, they became royal, they became soldiers, they became saints.
All this together grew up from this mantra.
Video courtesy of Sikh Dharma International.