drizzling rain, to soak (used fig. of favours)
霡 centers on light, soaking rain: a fine drizzle that gradually wets everything. The figurative sense of bestowing favors extends naturally from this idea of gentle, pervasive soaking.
霡 combines 雨 (rain) with a phonetic component historically related to 脈 (myaku), suggesting the sound and the idea of fine, vein-like drizzle. The exact historical development of the lower part is uncertain.
Under the rain 雨, the moon 月 shines on a long, eternal 永 drizzle that soaks everything gently. Picture a moonlit night with endless fine rain.
For バク, imagine a drizzle so fine it feels like a soft, wet blanket: blanket -> バク, and the rain soaks you like a damp cloth.