Simply put, the LOTUS is "you" as you believe your self to be: body, mind, emotions, personality, etc. The JEWEL is the Infinite Spirit that manifests as you, and your true nature.
This mantra has been called a mahavidya mantra, one capable of bringing about "The Great Knowledge" (Spiritual Illumination).
Origin: The first printed mention of this mantra occurs in the Sanskrit Karandavyuhasutra (tr: “The Basket's Display,” aka "The Noble Mahayana Sutra") complied at the end of the 4th century A.D. It occurs in Part Two, Chapter 5 and 6. The earliest (so far) written manuscuript I have found for this sutra is a 17th c. ms. in Sanskrit, Prachalit Nepal script (which has similarities to Gupta and Siddham scripts). Here it is, written as Om Mani Padma Hum - and NOT as Om Māni Pādme Hum, (Om Mah-ni Pah-dme Huhm) as often pronounced incorrectly.
Shakyamuni Buddha states, "This is the most beneficial mantra.
Even I made this aspiration to all the million Buddhas and subsequently
received this teaching from Buddha Amitabha."
If so, then this mantra was in the oral tradition at least 800 years before
the sutra was compiled, i.e. time of Buddha, circa 500 BC.