Don't mix them up

Two men dressed in red one with a beard the other with horns on his head

Both with the same name, one a Saint the other Old Nick, both of considerable fame

The bearded comes once a year while the horned one is always near

One sits on your shoulder the other you sit in his lap one never sleeps the other takes a nap

Through moral rifts or snow drifts, to the obedient both promise gifts