Given only 8 words to describe 'Flow', by Mihaly C. those would be my choice.
While very scientific in his approach, I think he gets to the core of what many of the new age fluffy, and old time dogmatic approaches get right and why, even if largely untrue, they help so many people find happiness. Creating order in a cacophony of thoughts. Allowing people to interpret events in a way that gives them hope.
He talks about 'psychic energy' in a way that captures the basis of my understanding of what the Yogi's describe as Prana. We are not in control of a lot of things, but by finding those things that we are in control of and by interpreting life's challenges in a constructive way, we can create opportunities for purpose.
'Purpose gives direction to one's efforts, but it does not necessarily make life easier. Goals can lead to all sorts of trouble, at which point one gets tempted to give them up and find some less demanding script by which to order one's actions. The price one pays for changing goals whenever opposition threatens is that while one may achieve a more pleasant and comfortable life, it is likely that it will end up empty and void of meaning.'