Ki Tisa - Love your wife

To understand what it means, "You must observe my Shabbat day," we need to look at the first letters of the words. 

אַךְ אֶת-שַׁבְּתֹתַי, תִּשְׁמֹרוּ כִּי אוֹת הִוא בֵּינִי וּבֵינֵיכֶם

The first letters are

  אשתך אהוב

or 

"Love your wife."

That means that a man must love his wife and be with her. Therefore, the following words start with the letters

וְשָׁמְרוּ בְנֵי-יִשְׂרָאֵל, אֶת-הַשַּׁבָּת

or

ביאה - intimacy.

What follows is

אֶת-הַשַּׁבָּת לְדֹרֹתָם

or 

אהל, tent, and that is always a hint to his wife.