The premise of Discipling by Jesus is that uniting with Christ is what enables us to become fully human, as we learn to love our Selves and Others as Jesus does.
God is love, and His presence permeates (and transcends) every being in the universe. The Father’s passion is for all creation to be fully aware of and aligned with His love — as Christ was even while on earth — which manifests in us loving each other as He loves us.
Anything that blocks the flow of His love in and through us is “sin” — a sign that part of our heart, soul, mind or strength has not surrendered to and received God’s love. To address this, Westerners tends to focus on proper thinking (“mind”), while the East emphasizes proper acting (“strength”). While often useful, those might not address blockages of the heart and soul.
In my experience, the most common such blockage is unprocessed pain, especially (but not only) from traumatic experiences during our formative years. We may often not be aware of that pain until there is a triggering event, and even then we may blame our reaction on the external event rather than our internal trauma.
While secular therapy can help, I believe the only real cure for such pain is the cross of Christ. Something about the blood of Jesus helps us get past the wounds we have received from others, as well as the shame and guilt of our own failures.
Having encountered Christ, of what must I repent to grow closer to Him?
That is why the arc of Discipling by Jesus climaxes with the Blood of Jesus in communion. The Word, Spirit & Body are there to help us see and embrace the chasm between the awesomeness of God and the poverty of our humanity; a chasm that can only be bridged by the grace released through repentance.