it was to these qualities and to some knowledge of the country that he owed his selection for his present perilous duty at the extreme outpost.
it was ...that ...是强调句句型
句中强调了to these qualities and to some knowledge of the country
句子还原成一般的陈述句是 he owed his selection for his present perilous duty at the extreme outpost to these qualities and to some knowledge of the country
其结构是he owed ...to ...
owe to 的意思是把……归功于……