Samandriel loved his Father.
When Heaven learned of Lilith's plan for Dean Winchester, Samandriel was part of the siege of Hell. He fought through demons and darkness because it was Heaven's order. Samandriel had done many things because they had been Heaven's orders.
As the angels lied and cheated in aid of the Apocalypse, Samandriel watched as only one of his brothers tried to stop it. Watched him side with humanity and turn his back on Heaven. Watched him punished.
When the Great Plan came tumbling down and the Apocalypse was stopped, Samandriel was glad. He did not lack faith in his Father's plan, but he did not believe this had been it. This was the angels' plan, and they had not deserved to win.
With Michael locked away, Heaven became a place of chaos. Samandriel hoped that his Father would return to set it right, but the angels did not look for him. Instead, they tried to take it for themselves. When Rafael seized control, Samandriel came to learn that Heaven was much more like Earth than he'd thought. It was only his Father's land if those within it lived by his Father's rules.
Samandriel did not fight Rafael. He did not participate in the affairs of Above at all. He was through with Heaven's orders. Instead, he spent his time caring for souls.
Some said Samandriel was too soft. That after all his time spent watching Earth he was in danger of falling into the trap of emotion, like that Castiel. But Samandriel saw it as his duty to care. Whether in Heaven or still on Earth, Samandriel valued human beings just as his Father had.
When questioned, he simply answered: someone had to.
When Castiel took over Heaven, Samandriel felt the death of every angel he smote in the name of discipline. He wanted to go to his brother and speak to him. But he wondered if perhaps his time observing Men had indeed gotten to him, because he was afraid. He wanted to pray for Castiel, but feared he was the only one who would hear them.
For a time, he did not pray. When Castiel fell, he prayed for his brother every night.
Samandriel knew of Castiel's fondness for the Winchesters. As a consequence, he kept an eye on those boys. In that way, he was able to keep an eye on his brother as well.
When Castiel and Dean Winchester were lost, Samandriel grieved. He was one of the few who did.