In SharePoint (on-premises or 365), you can get the embed code from a word or PowerPoint file and insert that in another page with the </> Embed Code ribbon command.
Unfortunately Excel Web App doesn't provide the option to generate this embed code. Fortunately you can create this very easily yourself.
Just get the URL for the Excel file and add ?web=1 to the end of it. This will give you the code that you place in a "</> Embed Code" by creating an iFrame from the Insert Ribbon of a publishing page, wiki page, blog article, discussion item, etc.
The embed code will look like this…
<iframe src="http://yoursite/Priorities.xlsx?web=1" width="100%" height="400px"></iframe>
It is possible that Excel Web app is not available if Excel Services is the default for viewing Excel files (A farm wide setting), in which case there is a Web Part called Excel Web Access which can be added to a page (Enterprise Site Features must be enabled).