Note:  This was originally written for posting on a Jewish list, so
I obviously didnt make use of the KJV or JST in presenting an 
interpretation.  The JST adds considerable text to the account and 
clarifies a number of issues that are otherwise ambiguous.  Everything
below the solid line is what was sent to the Jewish list.

JST Gen. 4                        KJV Gen 4
----------                        ---------
And it came to pass,              And it came to pass
that the Lord appeared unto him 
as he was in the way,             by the way
by the inn.                       in the inn,
The Lord was angry with Moses,    that the Lord met him,
and his hand was about            and
to fall upon him, 
to kill him;                      sought to kill him.
for he had not 
circumcised his son.
Then Zipporah took a sharp stone  Then Zipporah took a sharp stone,
and circumcised her son,          and cut off the foreskin of her son,
and cast the stone at his feet,   and cast is at his feet,
and said, Surely thou art a       and said, Surely a
bloody husband unto me.           bloody husband are thou to me.
And the Lord spared Moses        
and let him go,                   So he let him go:
because Zipporah, his wife, 
circumcised the child. 
And she said,                     then she said,
Thou art a bloody husband.        A bloody husband thou art,
                                  because of the circumcision.
And Moses was ashamed, 
and hid his face from the Lord, 
and said, 
I have sinned before the Lord.

_______________________________________________________________________

JPS rendering:

     At a night encampment on the way, the Lord encountered him and
sought to kill him.  So Zipporah took a flint and cut off her son's
foreskin, and touched his legs with it, saying, "You are truly a
bridegroom of blood to me!"  And when He let him alone, she added, "A
bridegroom of blood because of the circumcision."


     The exact manner of the manifestation of G-d to Moses is unclear,
was it theophany, hostile angelic messengers, was he stricken with
illness?

     Apparently while Moses was engaged in the confrontation, Zipporah
perceives the cause of it is Moses' failure to circumcise his son. 
Zipporah intercedes, presumably to spare the life of her husband given
the bridegroom reference.

     After circumcising her son, Zipporah touches something to Moses'
leg, whether it is the flint or the foreskin is unclear.  The touching
of the legs is probably indicative of some kind of oath, cp. Gen. 24:2-
3, 9.  In Exod. 24:8 Moses sprinkles blood on Israel and tells them it
is the blood of the covenant.  Regardless of what Zipporah touched to
Moses' legs, it was bloody and may have been used in a similar manner
(Zipporah was undoubtably familiar with covenant sacrifice as Jethro,
her father, was a priest and sacrificed, cf. Exod, 18).   Thus, Zipporah
may be confessing her willingness to follow the G-d of Israel by
circumcising her son and making an oath to her husband.  One has to
wonder if Moses wanted to circumcise his son previously, but she
resisted him because of her Midianite background.  Israel in general
continued circumcision while among the Egyptians (cf. Joshua 5), but
Moses lived mainly among Egyptians and then fled to Midian so he was not
among Israel.  Perhaps Moses was more acculterated to non-Israelite
views so he did not recognize the importance or necessity of
circumcision until this event.

     Assuming the oath hypothesis has merit, Zipporah would have
emphasized that Moses was her husband for two reasons.  One would have
been to attempt to legitimize the circumcision as she was Moses' wife
and the boy's mother.  The second would have been to show that she was
being faithful to her husband's G-d and they were united in their faith. 
Had Zipporah not interceded, the text tends to indicate that Moses would
have been slain and Zipporah would have been left a widow.  Instead, she
intercedes, saves her husband, and her marriage and endorses the G-d of
Israel by circumcising her son.