"There was evening, and there was morning - the first day."
A day in our traditional sense begins in the morning. We rise from our sleep, as the sun rise upon us, and then we labour. After a day's hard work, we commune and rest, as the sun rests from the horizon. Day and night, day and night.
However, in the Jewish tradition, God first created night, and then day, and therefore the Jewish day begins at nightfall, and ends at nightfall the next day. For the Jewish people, they begin their day in rest, and they labour and work from the foundation of having received rest. The cycle of day is fundamentally different, but why is this significant?
It is because God's design for the human life is different from how we now see it. We work because we needed to produce, and we rest because we're tired from our labour. However, God wanted His people to begin in rest, and truly rest upon the fact that He had already worked and set things in motion. The mindset of rest and work is therefore flipped upside down. We rest because we can rely on God's work, and we work knowing He has laid down it's foundation.
We were never meant to work out of a need to produce, and never meant to rest out of sheer exhaustion. God in His love for mankind created night, and then day, so that His people would rest out of assurance, and work upon His establishment. This order of rest-work is also mirrored later in the story of creation, when Adam, the first man, was created on the 6th day. Adam was created at the end of God's labour, so that he may enter into life on the 7th day, Sabbath (rest).
What would your life look like, if your day began in rest?