This also refers to Christians on housetops
and in fields outside of Judea (as does
Luke 17:31 in reference to the 2nd coming)
for the great tribulation will be on all
flesh in the entire world:
Matt 24:21-22
For then shall be great tribulation, such as
was not since the beginning of the world to
this time, no, nor ever shall be. And except
those days should be shortened, there should
no flesh be saved: but for the elect's sake
those days shall be shortened.
The elect is the Church:
Col 3:11-12
Where there is neither Greek nor Jew...
Put on therefore, as the elect of God,
holy and beloved, bowels of mercies...
1 Pet 1:2
Elect according to the foreknowledge of
God the Father, through sanctification
of the Spirit, unto obedience and sprinkling
of the blood of Jesus Christ...
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Matt 24:20
Pray ye that your flight be not in the winter,
neither on the sabbath day...
Some Christians do keep the Sabbath:
Rom 14:5
One man esteemeth one day above another:
another esteemeth every day alike. Let
every man be fully persuaded in his own
mind.
The parallel passage in Mark 13:18 doesn't
mention the Sabbath.