God spoke to Moses saying: When you take a census of the Israelites - literally, "when you lift the heads of the sons of Israel."
Why is counting referred to as "lifting of the head"? This has to do with the spiritual concepts that are represented by the hair of the head.
The upper Sefira of Keter, or Crown, has all ten Sefirot in it. Keter represents the Will. Before God created the world, He had to desire to do it. In order to have the desire to do it, He needed to have the desire for that, and so on. This includes an infinite loop and is a meditation device in itself.
Of the ten Sefirot, or ways in which God conducts the world, only Netsach and Hod - Victory and Glory, represented by the right and left legs in man's body, have the self-restricting judgment in them. The other eight continue to expand with kindness, and only these two can thus be made to come back as "Returning Light," bringing back with them the sparks of holiness that fell down. This is achieved by sweetening their judgments, by the power of Keter.
The hairs are like pipes that contain light, as in the letter Vav. The scalp of the head is analogous to the heavenly sphere, and the hairs, which make holes in the scalp, are analogous to the pipes, or letter Vav, transmitting spiritual influences below.
That is why the expression used is "when you lift the head of the sons of Israel" - to lift their head with the hair, to clear up the spiritual pathways from Heaven. This is achieved by counting, to which the hair is connected, by giving charity with the coin called Shekel - Weight, and by the various permutations of the Name of God. The hair also prevents the Evil forces from viewing the back of the head.
Art: Albrecht Dürer - Self Portrait in a Fur-Lined Coat