What do the last six commandments have in common that distinguish them from the first four?

The last six relate to the human race - the first four relate to god himself.

I am the Lord your God

You shall have no other gods before me

You shall not make for yourself an idol

Do not take the name of the Lord in vain

Remember the Sabbath and keep it holy

Honour your father and your mother

You shall not kill

You shall not commit adultery

You shall not steal

You shall not bear false witness