निमित्तमात्र

Nimittamatra means merely an instrument. In chapter 11 the Lord tells Arjuna to arise and be merely an instrument (Gita 11.33). The word occurs in that verse itself, so it is a word of the Gita.

The word "merely" matters. To be an instrument is nothing bad, but to be merely an instrument is to be the means, while the action is yours and the outcome is not made by you alone. The Gita says the same in other places. Actions are done by the qualities of nature, and only a mind deluded by ego says "I am the doer" (Gita 3.27). Five causes of an action are listed, and seeing only the Self as the doer is not seeing truly (Gita 18.14–16).

The Lord says this to Arjuna in the middle of fear, to lift a weight from him. Action is not taken away: "arise" is said.

Common misreading: that being an instrument is being a puppet, with no choice and no responsibility.

Better sense: action and responsibility stay one's own; what is given up is the claim of being the doer and the sole burden of the result. After the whole teaching the Lord also hands the choice back to Arjuna (Gita 18.63).

Read the whole passage in Merely an Instrument.