this saying has its origins in the 70s love movement and was made really famous by Cheech & Chong in the 80s through their marijuanha films.

It does not mean OMG or awesome. It's a stand-alone phrase, usually preceding the phrase that will describe the object or situation that's freaking you out, blowing you away or leaving you at a loss for words.

It's present tense, denoting something that's actually happening and feels like it is beyond incredible.
Holy mother of pearl! Look at those tender young asses(on the beach);- cops in helicopter shadowing Cheech & Chong.

Holy mother of pearl! That's some serious shit.

Holy mother of pearl! That's one strong fuckin drink.

Holy mother of pearl! Did you see that?(a flying dog playing a guitar and shooting laserbeams from its eyes)

A spaceship appearing over London would leave you speechless, probably only with the ability to utter the words 'holy mother of pearl.'
by Lanos Iceland July 28, 2011
(Walking through the halls of a very crowded school where freshmen feel it's okay to stand in the middle of the hall and make out)

"Holy mother of hell! Move it and get a room!"
by KayKaboom October 1, 2009
An expression used when one is astounded by a woman's large breasts.
"Look at Queen Latifah in that dress! Holy mother of jugs!"
by Brigitte April 1, 2003
Holy Mother of Balls is when an event is so profound, so amazing and awesome, that a single ball will not suffice, the Holy Mother of Balls needs to be referenced.
Holy Mother of Balls, did you just jump that gorge on your motorcycle?
by InkMan November 17, 2013