May unexpected good luck descend on you!
Spider + descending from the sky
‘Zhi zhu (蜘蛛, spider)’ has a nickname ‘xi zi (蟢子)’ or ‘xi zhu (喜蛛)’ meaning the ‘lucky one’ or ‘lucky spider’.
Its first character ‘xi 喜(蟢)’ for ‘happiness (good luck)’ is then combined with the phrase ‘cong tian jiang (从天降)’, meaning ‘descending from the sky’.
The whole phrase (喜从天降) describing the spider’s action in the picture is to convey the meaning ‘pleasant surprise descending on you’.
画面要素：蜘蛛 + 从天降
谐音机制 : 取蜘蛛的别名‘喜蛛’谐音‘喜’; 某物自天而降，取‘从天降’
Fig 1: fan cover, Xi Cong Tian Jiang, from Lu Xiang Yue, courtesy of the National Palace Museum, Taipei
Fig 2: illustration, Kisshō zuan kaidai : Shina fuzoku no ichi kenkyū by Nobuchika, Nozaki, Pl. 36, Tenjin: Chn̄goku Dosan Kōshi 1928
Fig 3-4: porcelain vase, Chongzhen period (1628 – 44), Ming dynasty, courtesy of the Museum of East Asian Art (Cologne)
Fig 5: close-up, fan cover, Southern Song (1127 – 1279), courtesy of the National Palace Museum Monthly No. 107 p. 16 p.4