His comments in relation to the new policy were very insightful.

in 是介词，表示"在...方面"或"关于"。 relation 是名词，来自动词 relate（关联、联系），意思是"关系、关联"。 to 是介词，表示方向或对象。 in relation to 是一个固定短语，意思是"关于、涉及、与...相关"，用于引出讨论的主题或对象。