We already existed before this world, because our creation was decided by God long before our actual creation. Before our creation we therefore existed in the thought of God, we who later turned out to be intelligent creatures of the Divine Word. Thanks to Him, we are very ancient in our origin, because ‘in the beginning was the Word.’
St. Clement of Alexandria
…the World-generating Reason also considered, in His mind’s great representations, the images of the world formed by Him, this world which was generated later, but, which, for God was present even then. Everything is before God’s eyes: what will be, what was, and what is now. For me such a division is set by time: that one thing is ahead, another thing behind. But for God all merges into one, and all is held in the arms of the Great Deity.
St. Gregory of Nazianzus
So I almost fooled you didn’t I (or rather St. Clement did)? Upon the first few words you were thinking, “What’s going on here?” But then you realized this is a much more lofty idea than some measly pre-existence of souls.