The motive of the executions would be to instil fear.

【翻译】执行死刑的动机是要灌输恐惧。

【分析】这个句子比较简单，它就是一个“主系表”结构。其中，不定式作表语。系动词be前的would表示“可能性”。又如：

The next best thing would be to tell him the truth. 其次，最好的办法就是把真相告诉他。

The wisest course would be to ignore it. 上上策是不予理睬。

The best thing for you would be to forget it.  你最好是把这事忘了。

The best thing would be to have a check again. 最好是再检查一遍。

My advice would be to do it at once. 我的建议是立刻就做。