It is not the first time that Maiden compose songs with strong relation to the Bible.The song itself speaks of sins, prays, and the penance of men. We will do a lyrics breakdown and compare them to a texts in the Bible.

We believe in that thou shall not kill
But others are ready to spill

Thou shalt not kill is a moral imperative included as the 6th of the Ten Commandments in the Holy Bible (Exodus 20:13, Deuteronomy 5:17).

The imperative is against unlawful killing resulting in bloodguilt. The Hebrew Bible contains numerous prohibitions against unlawful killing, but also allows for justified killing in the context of warfare, capital punishment, and self-defense.

So, even if killing a person should be avoided and forbidden, men are always ready to spill the blood of their fellowmen.

The hearts of all men since beginning of time
Living with temptation
Wanting and crime

Another Genesis reference: Adam and Eve has been tempted by the Serpent (Satan), wanting to be omniscient, eating the fruit from the Tree of Knowledge (this act was forbidden by God: so, they committed a crime.

According to this, sin exists since beginning of time.

Into the valley of death fear no evil
We will go forward no matter the cost
Into the valley of death follow me now
Bring me your souls and I'll make it our last

Here is a reference to Psalms 23:4:

"Yea, though I walk through the valley of the shadow of death, I will fear no evil: for thou [art] with me; thy rod and thy staff they comfort me."
The Psalm presents a man who puts his faith in God: besides him, he "will fear no evil". So, the song's character who speaks "follow me now/Bring me your souls..." is probably God.