Seeing a cardinal out your window isn’t uncommon, and may have a special meaning, depending on what you’re going through. Any of the aforementioned meanings may still apply, but the window is unique in that the cardinal is appearing to you in your home.
Our homes are our safe spaces, and our havens from the world. For a cardinal to show up there for you can indicate a need to tap into your own energy and power to keep your home (and subsequently, your own aura) safe and secure. Perhaps that means setting firmer boundaries, working with your root chakra as previously mentioned, or facing any fears you’ve been avoiding.
Again, as Charles explains, you can always directly ask/invite a cardinal to work with you and share its messages, to get a better understanding of what it’s trying to tell you. And from there, you can heed its message and take appropriate action.