And they have defeated him by the blood of the Lamb and by their testimony. 

Revelation 12:11

So Jesus is saying to us to regularly announce, tell, declare, to make a show of, to lift up the banner of victory He purchased with His blood, to raise it high, to wave it high, to not be silent about it…… Since partaking of the communion is obviously not a loud event (physically), this proclamation/declaration is  something like a silent noise