He often does act through people - after all, a physical presence is often required, but he can work independently of humans.

We heard an amusing story of a family in Nepal whose 'allottment' (as it were) was in the middle of the area that the villagers used for their own crops. When the family became Christians, the other villagers decided to block the network of irrigation channels that ran through the area where they touched the family's plot. A week or two later, as the level of the river that fed the channels dropped and the channels dried up, the family's plot was the only one that stayed damp. This wasn't a normal yearly event; the villagers had no recollection of it happening in their life times. Somehow water was making its way underground to it, but by-passing all the other plots. They had to unblock the channels in order for the water that was reaching the one plot to reach the others. OK, it might have been coincidental, but the timing suggests that there was something more than that - what some call a God-incident.