The Lord within
I will put my laws in their minds
and I will write them upon their hearts.
I will be their God,
and they shall be my people.
And they shall not teach,
each one his fellow citizen and kin, saying,
"Know the Lord,"
for all shall know me,
from least to greatest.
Indeed, as baptized and confirmed Christians we have the Holy Spirit within us as our advocate and guide with gifts of wisdom, knowledge, and fear of the Lord.
The challenge, however, is that there is more in the human heart than just the law of the Lord: there are also desires and temptations that are not of God. Indeed, some people use passage such as this to reaffirm their own egocentricism and their own subtle hedonism (for them, they themselves are the lord within).
As always, we need to exercise discernment: to ask the Lord Jesus to help us with the grace of the Holy Spirit so that we may see past the clutter of earthly desires and confused philosophies and may recognize clearly within our hearts the law of the true God and Lord of the Universe.