Here's a broader view of the image. It's an early Greek vase known as the "Chigi vase", dating to the 7th century BCE. It is often thought to be the first pictorial depiction of hoplite combat. (That has been disputed, though; the Wikipedia article mentions a few elements of the dispute. The objections are very unpersuasive to my mind).

The painting is a classic example of the Archaic/Classical Greek practice of using a single image to portray multiple moments in a narrative. The "story" begins at the far left. The first figure is arming for battle, and is in the process of putting on his greaves. The second figure has his greaves on and is putting on his helmet. The third is fully armed, having also picked up his spear and shield, and runs to take up his position in the hoplite rank. The rest of the rank is running (notice the raised rear feet), kept in formation by the musical cue from the aulistes (the boy playing a set of pipes; these pipes were reed instruments, not unlike a pair of oboes, and very loud). Carrying on to the right, the next rank has now stopped running and has raised their spears, and we finally get the clash between the two lines.

The clarity and thought put into the design is really remarkable. There are a couple of hiccups: the first rank of hoplites (the ones running) only have one spear each, while the soldiers at the far left and the ones already in battle have two; and the two soldiers at the far left are putting on their equipment in different sequences (one has put on his helmet first, the other has put on his greaves first).