The core of this formula is concatenation using the ampersand (&) operator:
="The date is"&date
However, if you simply join a date with text and don't control the date format, the date will revert to it's raw serial number format, and the result will look like this:
"The date is 42887".
To control the date format, use the TEXT function, which is designed to convert a number into text using a specified number format. This article shows a list of codes you can can use for date formats.