Perhaps many do not understand that the first day of Unleavened Bread did not begin as a
holy day.  That is the reason that it was not wrong for the Israelites to travel on that day.  
It was later, perhaps as early as the following year that God established a holy day as a
memorial of what He did on the 15th of Nisan, for the Israelites.

Notice the wording of Exodus 12.42:
“It is a night to be much observed to the Eternal for
bringing them out from the land of Egypt”.
 The wording of this Scripture indicates that Moses
wrote this statement later – looking back on an event in Israel's history.  Evidently,
Moses did not write this statement before it happened!  It was in their future generations
that the Israelites were to observe the night in remembrance of what happened in their

Exodus 12:42 It [is] a night to be much observed unto the LORD for bringing them out from the land
of Egypt:
this [is] that night of the LORD to be observed of all the children of Israel in their

There are two points to notice here.  #1-why) the observation is for bringing them out of
Egypt – made possible by the Passover.  #2-when) the observation was for the time when
their ancestors came out of Egypt.  One does not make the day following an event a
memorial day.  If God destroyed the firstborn of Egypt on the 14th, then the memorial
should be on the 14th.  However, the memorial is on the 15th of Nisan, the night that the
destroyer passed over the home of the Israelites and destroyed the power of Egypt so
they could come out of Egypt.  That would be similar to the Americans celebrating July
5th for signing the Declaration of Independence on July 4th.  It would be like celebrating
one's birthday on the day after one was born.  The Israelites’ independence from Egypt
began during the night of the 15th of Nisan and they left the following morning of the 15th
(Numbers 33:3), therefore, the memorial of that event is on the 15th of Nisan.  The
Israelites did not leave Egypt on the 14th of Nisan.  Why celebrate leaving Egypt on the
15th, if God brought them out of Egypt on the 14th?

God did not establish the holy days of Israel until the Israelites were in the wilderness.  
After a great event happens, then one looks back on it and establishes a memorial.  

A good example is July 4th, a memorial of Independence Day.  The event happened, and
then yearly thereafter – at least after the founders won independence – the day was
memorialized because it was such a great event.  One does not establish a day to make
holy without some reason for doing so.  In other words, one does not establish a memorial
in advance.

The bible is very clear as to which day the Israelites started their journey out of Egypt,
the day that God later memorialized, according to Exodus 12:42.

Numbers 33:3 And they departed from Rameses in the first month, on the <fifteenth day> of the first
month; on the morrow (morning) after the Passover the children of Israel went out with an high hand
in the sight of all the Egyptians.

According to the bible, the Israelites departed from Rameses, their home in Egypt, on the
15th day of the first month.  They started out of Egypt on the 15th day of Nisan.  The
feast day would be on the 15th day of Nisan as a memorial of what the Eternal did on that
night and day to bring them out.

This is so clear that no one should be confused.  Paul makes it plain in his writing:

1Cor 5:7  Purge out therefore the old leaven, that ye may be a new lump, as ye are unleavened.  For
even Christ our Passover is sacrificed for us: {is sacrificed; or, is slain}
8 Therefore let us keep the feast, not with old leaven, neither with the leaven of malice and
wickedness; but with the unleavened bread of sincerity and truth.  {the feast: or, holyday}

The feast follows the sacrifice.  The feast is not the sacrifice itself.  The feast was to
begin, after the lamb was slain, at (toward) evening – therefore, the feast began on the
15th of Nisan.  In addition, God made it a Holyday after the event, not before.