In numerology, the number 40 indicates transition or change; the concept of renewal; a new beginning.
Some scholars believe the number 40 was originally sacred to the Jews and Muslims due to the fact that the planet Venus forms a pentagram in the night sky every eight years and returns to its original point every 40 years with a 40 day regression.
Possibly one of the reasons '40' was chosen (as opposed to another number), but idiomatically, it just refers to a long period of time.
Seemed important enough in the geno.
(40) ~ generations ~ Lk3:23
Now Jesus himself was about thirty years old, when he began his ministry. [Baptism]
He was the son, so it was thought, of Joseph, and the son of (40th) Heli, "or Eli" [Mary’s father?]
Lk3:24
the son of (39th) Matthat,
the son of (38th) Levi,
the son of (37th) Melki,
the son of (36th) Jannai,
the son of (35th) Joseph,
Lk3:25
the son of (34th) Mattathias,
the son of (33rd) Amos,
the son of (32nd) Nahum,
the son of (31st) Esli,
the son of (30th) Naggai,
Lk3:26
the son of (29th) Maath,
the son of (28th) Mattathias,
the son of (27th) Semein,
the son of (26th) Josech,
the son of (25th) Joda,
Lk3:27
the son of (24th) Joanan,
the son of (23rd) Rhesa,
the son of (22nd) Zerubbabel,
the son of (21st) Shealtiel,
the son of (20th) Neri,
Lk3:28
the son of (19th) Melki,
the son of (18th) Addi,
the son of (17th) Cosam,
the son of (16th) Elmadam,
the son of (15th) Er,
Lk3:29
the son of (14th) Joshua,
the son of (13th) Eliezer,
the son of (12th) Jorim,
the son of (11th) Matthat,
the son of (10th) Levi,
Lk3:30
the son of (9th) Simeon,
the son of (8th) Judah,
the son of (7th) Joseph,
the son of (6th) Jonam,
the son of (5th) Eliakim,
Lk3:31
the son of (4th) Melea,
the son of (3rd) Menna,
the son of (2nd) Mattatha,
the son of (1st) Nathan,
the son of David,