In Chains, as grandfather speaks quietly to Isabel and kisses her scar, what do his words mean?

At the Tea Water pump, a group of slaves are arguing over which side in the war will give them their freedom. Grandfather, who operates the pump, laughs and says that neither side will. The only way that the slaves will obtain their freedom is through faith, a point he illustrates by reference to the River Jordan in the Bible, which the Israelites crossed to gain entrance to the Promised Land.
Isabel has a scar which acts as a permanent reminder of her servitude. But Grandfather tells Isabel that she should not be ashamed of her scar, and as he kisses it, says that a scar is a sign of strength, a sign of a survivor. What he means by this is that Isabel has come through a lot, and that what hasn't killed her has only made her stronger. Far from being ashamed of her scar, Isabel should see it as a mark of her strength and fortitude.