Theistic religions expand the religious domain to include hypothesised external entities.
In essence they believe “we are not alone” and this assumption should impact of our actions.
A succinct expression one ethical religion is given
in the Christian Bible, Matthew 22:37
“Thou shalt love the Lord thy God with all thy heart, and with all thy soul, and with all thy mind. This is the first and great commandment. And the second is like unto it, Thou shalt love thy neighbour as thyself. On these two commandments hang all the law and the prophets.”
Matthew 22:37-40
There are three elements here, Self, Neighbour And God.
Self we cannot escape.
The recognition of Neighbour is essential for survival, but optional for belief.
God may seem a great jump.
However, once we opt to recognise a single consciousness outside ourselves (and our individual experience of time), our religious domain is plural and possibly infinite.
The sum total of this greater scope (across time) is a simple, but useful definition of God.