The poem
So Abram rose, and clave the wood, and went, And took the fire with him, and a knife. And as they sojourned both of them together, Isaac the first-born spake and said, My Father, Behold the preparations, fire and iron, But where the lamb for this burnt-offering? Then Abram bound the youth with belts and straps, And builded parapets and trenches there, And stretchèd forth the knife to slay his son. When lo! an Angel called him out of heaven, Saying, Lay not thy hand upon the lad, Neither do anything to him, thy son. Behold! Caught in a thicket by its horns, A Ram. Offer the Ram of Pride instead.
But the old man would not so, but slew his son, And half the seed of Europe, one by one.

The father's refusal of the sacrifice that would save his son is a powerful analogy of how mankind refuses the sacrifice of Jesus that was provided for all, so we could receive the Spirit that enables us to defeat the desires that lead to all hurtful words and actions that create distrust, hatred, war, and an endless list of evils.
Siegfried Sassoon persuaded Owen to omit the final line from his finished copy, though this is one of the most powerful lines of the Poem
This poem is confusing, but thats my dad for you.
This poem is about the horrors of war.