"He realized the true purpose of Budo was love that cherishes and nourishes all beings."
The binding feature was O'Sensei's concept of Budo. The four methods you mentioned in your post all have to do with nourishing.
1.Martial methods for protection from harm.
2.Farming methods for sustenance.
3.Spiritual methods for the relationship with God ( or whatever your religious beliefs are).
4.Community methods for the relationship with others.