In this sense, it means to gain some control over something. You harness an ox to pull a plow through a field: this is the original, literal meaning. The metaphorical meaning is that humans become able to master or control an outside force.

Quite poetic and seemingly characteristic of the philosophical writings of Pierre Teilhard de Chardin. I find such ethereal writing hard to grasp, define or even to make sense in our modern age. One thing to keep in mind, this English is translated from French.

harness energy 套马 = to harness a horse In the same way, we harness energy and guide it so it becomes useful for us.