For example, one's choice of a marriage partner is not only an emotional matter, but at heart a doctrinal issue. God has ordained that marriage reflect the unity that exists between Christ and His Church. Such close unity cannot exist between a believer and an unbeliever. Further, the doctrine of the covenant involves that God entrusts His covenant children into the care of believing parents, so that these parents might in turn teach God's children His ways. Right doctrine produces right ethics.
Right doctrine determines the way one lives.
If one errs in doctrine, this will be evident in his life, and vice versa. The Belgic Confession contains many doctrines.