काल

Kala means time. In chapter 11 Arjuna asks who the fierce form is, and the Lord says: I am Time, the destroyer of worlds, grown vast, and I am now engaged in gathering the worlds in (Gita 11.32). Here Time is a name the Lord takes for himself.

The name does not appear only here. In chapter 10 he says that he alone is imperishable Time (Gita 10.33). In chapter 8 the world's coming and going is described like day and night (Gita 8.18–19). So in the Gita Time does not only destroy. It also makes, upholds and gathers in.

In chapter 11 the mention of Time tells Arjuna that his fighting or not fighting does not decide the fate of these warriors. It is after this that "be merely an instrument" is said.

Common misreading: that Time here is only the clock, or the name of another deity.

Better sense: Time here is the Lord's own power. It does not mean that anyone's violence is made right. It means that Time does not wait for Arjuna's decision.

Read the whole passage in Merely an Instrument.