Rules for writers, Tenth edition - Diana Hacker, Nancy Sommers 2021

Use a colon after an independent clause to direct attention to a list, an appositive, a quotation, or a summary or an explanation
The colon
Punctuation

The colon is used primarily to call attention to the words that follow it, such as in the following situations.

A LIST

The daily routine should include at least the following: ten minutes of stretching, forty abdominal crunches, and a twenty-minute run.

AN APPOSITIVE

My roommate seems to live on two things: sushi and social media.

A QUOTATION

Consider the words of John Lewis: “Never, ever be afraid to make some noise and get in good trouble, necessary trouble.”

A SUMMARY OR AN EXPLANATION

Faith is like love: it cannot be forced.

NOTE: When an independent clause follows a colon, beginning with a capital letter is optional. Some disciplines use a lowercase letter (Faith is like love: it cannot be forced). See also 46f.