First, all
ten commandments “hang” from the same main branch: God's
character (Matthew 22:37-40). God is the center of all commandments,
not the laws themselves. The commandments exist for His glory and
delight and they are an expression of God himself (Jeremiah 9:24-26),
a way to know him. Therefore, obeying all those commandments is to
give testimony of him, to point to him and also to love him (John
14:21). The law, then, promotes knowledge of God and conformity to
him, which leads to righteous deeds. All righteous deeds arise from
love or hate of God.
Secondly, the content of each commandment overlaps that of others in
such a way that all commandments interpret each other. The
understanding of adultery as wrong and faithfulness as right helps us
understand why idolatry is wrong, when we see it as a kind of
unfaithfulness (Ezra 16, Hosea 1-3). When we understand that
worshiping God only is right and act accordingly, we also understand
we're not supposed to make images and worship them. Since all
commandments are perspectives on the ethical life attached to the
same base-principle – God's character - one can't break one
commandment without breaking this base-principle and all that flows
from it, that is, all the other commandments.
Thirdly, all commandments and their explicit applications form a
coherent ethical system that covers all areas of life. Some of those
applications are cited in detail in Scripture, addressing practical,
real life situations of a given time and serving as models for our
own contemporary applications (as used by the writers of the
Westminster Confession of Faith and Catechisms). They're called case
laws. Case laws in general and their particular subtypes (like
penal laws) develop the Decalogue by expanding the range of
application of a commandment. The fifth commandment, for example,
teaches the overarching principle of honoring father and mother . The
case law derived from it, thus, expands this principle by showing
that we should also honor elders. The sixth commandment's expansion
accounts for laws on self-defense, on accidental kill, on caring for
other people's lives by building parapets, and so forth. The seventh
commandment, when expanded, originates a whole sexual ethic. The
eighth commandment is expanded by case laws on generosity, honest and
hard work and providing for the poor, while the ninth is developed in
such a way that it allows the legal system to function, due to the
warnings against corruption. Other examples could be cited, but these
will suffice.
Finally, all ten commandments teach us to love our neighbor like
God loved us (John 15:12). The whole Decalogue was summarized by
Jesus in Matthew 22:37-40: “love the Lord […] and […] love your
neighbor as yourself”. Only by obeying all the commandments one can
perfectly love the Lord and consequently love his neighbor. But no
man has ever kept the whole law except Christ. Therefore, conforming
to Christ is conforming to the Law, and obeying him is obeying God's
law (John 14:21; Ephesians 5:1-2). Only imitators of Christ can show
true sacrificial love (Romans 15:2-3), with a heart willing to
forgive, serve and suffer selflessly in humility for the sake of
their neighbor.