It was caused by the human need for closeness, Castiel was sure. There seemed to be no other reason for it.
Holding hands just seemed so impractical. Humans were very dependent on using their hands for, well, most everything, and using one of them to grasp another person’s just rendered both of them more helpless.
Hands were excellent tools, really. Four fingers and a thumb to grab and grasp, curling together and inwards to make a weapon, shielding, sensitive fingertips to explore and assess a wide range of materials. Sometimes, Castiel found himself studying Sam’s palms, the thin scar-like lines that didn’t have all that much of a function somehow fascinating.
Castiel wondered why he didn’t. Sam was human and should want closeness sometimes, shouldn’t he? Castiel supposed he could indulge Sam and hold his hand in times they weren’t needed for any tasks, and would respectfully inform Sam how impractical hand holding was when things needed to be done. He was fully prepared for the time Sam’s hand would grasp his in the name of romance; he would squeeze Sam’s hand back and smile to signal his continued affection. Castiel could indulge such a human need sometimes, if Sam required it. They were romantically involved (”Dating,” Dean said, although they spent most of their time together in whatever motel room Sam resided in at the moment) so Castiel was sure Sam would soon try to hold his hand. Humans did that.
After two weeks, they kissed for the first time and Castiel found himself not minding the physical closeness, the hand at his jaw, Sam’s lips against his. And in the days after, he found himself even more enthralled by Sam’s hands. Their little movements when he was reading, or sweeping along the table, or fingernails drumming repeatedly against the side of his coffee cup. Those were the moments he could study them without Sam noticing, he hoped. He wanted to know how the skin would feel against his own hand.
He was lost in how an unoccupied hand lay on the table beside the book Sam had been reading for the past ten minutes, drumming lightly against the table now and again, when Sam caught him.
“Something on your mind, Cas?” Sam asked and curled his fingers so they scratched against the surface with a soft sound. Castiel wanted to ask him why he wouldn’t hold his hand, why he wouldn’t take it when they walked beside each other, when Castiel was fully prepared to let him?
Impractical human need. Maybe it wasn’t. Maybe it was, but still-
“I think… I would very much like to hold your hand, Sam,” Castiel replied as calmly as he could, and it wasn’t as much of an epiphany as it was a dull realization of obviousness.
Sam’s eyes widened and his lips quirked up in a smile. “Well, you have my permission Cas. Come here,” he said and motioned to the chair next to him, leaving his open palm in invitation on the table. Castiel hesitantly took a seat before shifting his own hand on top of Sam’s (an unfamilliar gesture,but one he felt he could get used to). Sam went back to reading while Castiel silently marveled at the smooth texture and rough edges of Sam’s palm and fingertips, small scars making their way inbetween. He experimented with intertwining their fingers and it surprised him how right it felt, just the small physical connection with the human he adored.
“I thought you wouldn’t see the point of it,” Sam later answered when Castiel wondered if Sam actually didn’t like holding hands, and when Sam assured him he did, why he hadn’t asked Cas if they could. “You’re an angel, and I guess hand holding’s kinda… human.”
Castiel wasn’t sure if he liked it despite that, or just because of it.
Nevertheless, Sam held his hand.