Duncan's War by Douglas Bond

"Stumbling's of more than one kind, Duncan, m'lad." He stopped cutting and looked earnestly at his son. "Stumblings of heart, mind ye, break more than bones. Aye, guard yer heart, lad; guard yer heart. Ye can seem to keep the Covenant with yer hands and feet. that's the easy part, but if yer not keeping Covenant with yer heart, ye can't be honoring King Jesus."