5x22 Swan Song. A reminder that upon realizing his charge was dissatisfied with the ending, Castiel asked Dean what he wanted, charged back to hell to save Sam, brought him to Dean before peacefully retiring to heaven. He wanted Dean to be happy regardless of the rules. Peace or Freedom? Sam.
Season 15: peace or freedom? Sam.
Also season 15: happiness? Cas.
I am constantly wondering - HOW? How did Cas do it? The cage is the place to hold the archangels. And the archangels are second only to God in power. No one but God can go there. And Death. That's why I think that Chuck, Death, Amara are beings who live on a different level of the universe. But more on that another time.
So, when Sam decided to contact Lucifer, he needed the help of the most powerful witch on the planet. And then, they did not open the cell, but only slightly weakened the barrier, thanks to which Lucifer was able to manifest at our level of existence.
No one but beings like God can enter the cage. How did Cas do it? He entered the cage, found Sam, and exited the cage, taking the body with him. Sam's soul remained in the cage, but Cas couldn't have known it. I have a theory that the cage is like Purgatory. It is intended for beings such as angels and archangels, but not for humans. Therefore, the Cage, like Purgatory, seeks to push the person out.
Well, the soul, its origin is unknown to us, but perhaps it essentially consists of approximately the same as the angels. So without additional support such as Rowena's spells, the cage's defense kept Sam's soul inside.
And that, my friends, is a very good indication that Cas may turn out to be beings like Chuck, Death, Amara. Or perhaps a real God. Cas just forgot who he is.