He states here principles of reciprocity and karmic law.
"The Lord Loves the one that loves the Lord."
Now, I'm going to bet that as George would deepen in his spirituality through the years, he would also assert that the Lord loves the one that doesn't return the Lord's love. But the overall point of this song is that we humans get back in this universe to the measure that we give.
"And the law says whatever we do's gonna come right back on you."
This song culminates in what I personally will rank as one of the top five guitar solos by George in any song, solo or Beatles.
If you've never heard this song, stay for the ending, where his guitar just sings.