Teach only love for that is what you are.

这句话若加上标点符号会比较容易理解,如下：
Teach only love,for that is what you are.
或
Teach only love - for that is what you are.
Teach only love = 只教授 "爱"
for that is what you are = 因为你就是那个东西 = 因为你就是爱
所以,整句的意思是：只教授 "爱",因为你本身就是爱.
这句子在语法上没有错,但具体意思必须配合上下文才清楚.单独一句地看,有点莫名其妙.

教授只会爱上你是什么。