That they responded immediately and with great consternation is undeniable, as these were primary among those who would forswear and abandon their oaths. The term Recreance was not then applied, but has since become a popular title by which this event is named.
–From Words of Radiance, chapter 38, page 6
In Vorinism, it is accepted that the Knights Radiant became corrupt and betrayed humans to the Voidbringers. How they did this is unclear, as Knights are seen at the end of the last Desolations. It is also implied that they did this for their own power and desire to rule.
Due to Dalinar's visions and comments made by Teft, this is likely nothing more than overexertion or a downright lie, though Syl notes that "the Knights changed." This could mean that there is some truth to what the Vorin church says but likely nothing like the whole truth.
During one of Dalinar's visions, he appears to see the Day of Recreance, from the point of view of a soldier at Feverstone Keep. He notes nearly three hundred Shardbearers gathering near the keep. The Radiants proceed to drive their Shardblades into the ground and remove their Shardplate, leaving them for any to claim. Dalinar notes that when they abandon their Shards, the artifacts lose their glow. Soldiers from Feverstone then begin rushing out to claim the Blades and even fight each other and their officers for them.
When Dalinar asks one of the Radiants why they are abandoning mankind, he didn't reply but the Almighty responds, " ... I cannot be of that much help to you. The Night of Sorrows will come, and the True Desolation. The Everstorm."
This event allowed normal men to gain both Shardblades and Plate. In addition, it encouraged men to kill one another because there weren't enough Blades for all of them. It also horrified the spren, who ceased bonding to humans after this event as it had killed entire spren populations. Effectively, it meant the end of the Knights Radiant or the order in its pure form. There are hints that the order went on after this event but only for very short time.
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