Beginning of the End - Ellen G. White

Appendix
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Note 1, page 124: One of the important reasons why the Lord
delivered Israel from slavery in Egypt was so that they could keep
His holy Sabbath. The Egyptians did not give them religious liberty,
so the Lord "brought out His people ... that they might observe His
statutes and keep His laws." Psalm 105:43-45. Evidently Moses and
Aaron renewed the teaching about the holiness of the Sabbath,
because Pharaoh complained, "'You make [the people] rest from
their labor!'" Exodus 5:5. This would indicate that Moses and Aaron
began a Sabbath reform in Egypt.
The Lord told the Israelites that in keeping His Sabbath day,
they should "'remember that you were a slave in the land of Egypt,
and the Lord your God brought you out from there by a mighty hand
and by an outstretched arm; therefore the Lord your God
commanded you to keep the Sabbath day.'" Deuteronomy 5:15.
But Sabbath observance was not to be a commemoration of
their slavery in Egypt. Observing it in remembrance of creation was
to include a joyful reminder of deliverance from religious
oppression in Egypt that made Sabbath observance difficult. In the
same way, their deliverance from slavery was forever to kindle in
their hearts a tender regard for the poor and oppressed, the fatherless
and widows: "'Remember that you were a slave in Egypt, ...
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