Clue: Excess of devoutness — not the first — on Jewish Sabbath (7)
Answer: SATIETY
Explanation: Definition: Excess
 "piety"(devoutness/religiousness or reverence) **minus ****its 1st letter**(not the first) **placed after**(on) SAT(abbrev. for "Saturday" in the civil calendar, on which the Jewish Sabbath/day of rest falls).
Defn: …/surfeit.