The days of the week
Hebrew counts its days towards Shabbat. Each row gives the full phrase, the ordinal word alone, and the form Genesis 1 uses.
The first day of creation: God said ‘Let there be light,’ separated light from darkness, and called them Day and Night (Genesis 1:3-5). Genesis does not call it ‘the first day’ but ‘one day’ — יום אחד — the ordinal count used for the other five days begins only with the second.
The second day: God made a firmament to divide the waters above it from the waters below, and called the firmament Heaven (Genesis 1:6-8). Uniquely among the six days, Genesis does not close it with the words ‘and God saw that it was good.’
The third day: the waters under the heaven were gathered so dry land appeared, called Earth and Seas, and the earth brought forth grass, herbs, and fruit trees (Genesis 1:9-13). It is the only day on which Genesis repeats ‘and God saw that it was good’ twice — once for the dry land and seas, once for the vegetation.
The fourth day: God made the two great lights and the stars, set them in the firmament to give light on the earth, divide day from night, and mark seasons, days, and years (Genesis 1:14-19). Genesis does not name either light ‘sun’ or ‘moon’ here, calling them only ‘the greater light’ and ‘the lesser light’ (Genesis 1:16).
The fifth day: the waters swarmed with sea creatures and every kind of winged fowl, and these are the first creatures Genesis records God blessing, with the words ‘be fruitful, and multiply’ (Genesis 1:20-22). That blessing of living creatures is repeated only once more, for humanity on the sixth day — the seventh day is blessed too, but as the day itself, not a creature (Genesis 1:28; 2:3).
The sixth day: God made the beasts, cattle, and every creeping thing, then created humanity, male and female, in His own image, to have dominion over the earth’s creatures (Genesis 1:24-28). At its close Genesis calls the whole of creation not merely ‘good,’ as each earlier day was, but ‘very good’ (Genesis 1:31) — and this is the only day named with the definite article, ‘the sixth day’ (יום הששי), rather than a bare ordinal.
The seventh day, on which God finished His work and rested from all that He had made; God blessed this day and made it holy, because in it He rested from all His work of creation (Genesis 2:2-3). It was later commanded at Sinai — ‘remember the sabbath day, to keep it holy’ — grounded explicitly in this same act of creation (Exodus 20:8-11).