The heart of the matter is that God is after our hearts.
Love is one of the most powerful (if not most powerful) motivators. Human beings are “wired for love”. We were designed to set our affections and desires on something.
The human heart deplores a vacuum and it does a good job filling it with something. We ALL end up setting our affections on something.
Jesus is saying that the heart of the matter is a matter of the heart.
Following Christ can be difficult and counter cultural. In fact, following in the way of Jesus will many times set you against norms/values/expectations of the culture. If love for God isn’t our primary motivation for why we do what we do; why we follow Jesus we will get sidetracked/burnt out/ lose our way/ lose our faith.
God always has been after the hearts of people. He’s not after mindless robots. He’s not after religious converts. He’s not after loyal subjects. He’s after people’s hearts; after our love.