The chapter opens by quoting military people rather than speaking in its own voice: there is a saying among those who use arms. What follows is a preference for the defensive position stated in the idiom of hospitality. I would rather be the guest than the host, and rather retreat a foot than advance an inch.
The metaphor is worth keeping. A host has prepared, has committed his household and has to see the occasion through; a guest arrives, observes and can leave. Applied to a campaign it means declining to be the party that initiates, and the second clause makes the asymmetry explicit by trading a large withdrawal for a small advance.
Then four paradoxes describing what such a war looks like: marching without marching, rolling up a sleeve with no arm bared, seizing without a weapon, advancing where there is no enemy. Each names an act of aggression with its content removed, and the last is the summary. The ideal engagement is one where the opposing force is not there to be met, which is the same claim chapter sixty-eight makes when it says the one who is good at overcoming the enemy does not engage him.
The chapter then names the fatal error, and it is not cowardice. There is no calamity greater than taking the enemy lightly, and taking the enemy lightly nearly costs me my treasures. Those are the three treasures of chapter sixty-seven, which makes the two chapters continuous: contempt for an opponent destroys compassion, thrift and restraint together.