Hola Angel, If you translate the sentence literally it means "I left [to/for you] your keys. I [Dejé] is the subject, Te is the object.

In English we wouldn't bother mentioning the object; "I left your keys" would be fine, but in written Spanish it is necessary, because we need to know who is the direct object, and whether it is an individual you, him, her ... or group of people, you plural or them.

I don't know if it is acceptable when spoken colloquially to leave out the Te etc, but if you were speaking directly to the person or group of people I'm sure it would be understood at the very least. Saludos. John

thank you very much John. Appreciate your consideration