If you want to keep any post always on top and on home page, you need to stick that post. In WordPress, you can make any post as sticky post.

In the “publish options” click “Edit” link of visibility option.

The visibility options will expand. Now check the box “Stick this post to the front page” and click ok button.

when you will publish this post, it will be a sticky post.

To make it a normal post, edit the post and uncheck the box “Stick this post to the front page” and Save the post.