Introduced in Season 4 of Supernatural, Castiel quickly turned into a fan-favorite character. Fans fell in love with his clueless and naive celestial being persona, especially enjoying his relationship dynamic with Dean.
Castiel's character saw the most dramatic evolution, as he turned from a heartless soldier of heaven to a loving and caring friend and father. Supernatural is known for its great dialogues and quotes. Since Castiel had arguably the most interesting character arc in the show, he has some of the most wonderful quotes.
Badass Angel
"I Am An Angel, You Ass".
In the episode, "The Man Who Would Be King" in season 6, Crowley comes to Castiel and tells him about his mission of collecting souls. To this, Castiel retorts, "I'm an angel, you ass. I don't have a soul".
This was the time when Castiel's faith in God had almost vanished and so, this made him into someone who didn't care about anything anymore. Fortunately, it also escalated his sassiness as is evident in the quote. He doesn't restrain his impudence at all in this case because it's Crowley he is talking to and angels and demons never quite see eye to eye.
Being A Cute Nerd
"Why is 6 Afraid of 7? I Assume It's Because 7 Is A Prime Number And Prime Numbers Can Be Intimidating".
In season 9 episode 22, "Stairway To Heaven", Sam and Cas are trying to get into an old building. While referring to an Enochian code written above the door, Castiel says with a serious face as he usually does, that 6 would find 7 intimidating because it's a prime number.
He guessed the riddle wrong as Sam points it out, but it nevertheless makes up for an amusing scene. It is interesting to see how Castiel's fumbles and silliness only make him seem more endearing. The reason probably is the way Misha Collins plays him because as the series progresses, the angel becomes more and more charming and sweet.
Angel Sass Combined With The Dean Influence
"Hey, Assbutt!"
"Swan Song" or the season 5 finale was initially supposed to be the last episode of the show and thus, it had some of the most amazing heartfelt moments. However, Castiel delivered a memorable line that provided much-needed comic relief.
While Michael and Lucifer are going to battle each other, Cas calls after Michael, "Hey, assbutt," and throws a bottle of holy fire at him. Obviously, no such word or phrase exists but Castiel was attempting to be sassy and imitate Dean, who uses such offensive language often. Even though he fails horribly, it ended up eliciting a few laughs out of the audience in a much somber episode.
Advice On Managing Grief
"The Point Is That They Were Here At All And You Got To Know Them. When They're Gone, It Will Hurt, But That Hurt Will Remind You Of How Much You Loved Them".
There is a heartfelt scene in episode 14 of season 14 when Jack is worried about Dean and the idea of losing his loved ones is making him upset. Castiel helps him to come to terms with death by telling him that death doesn't mean the end of your relationship with your loved ones and even when it hurts, it will remind you of your love for them.
This is such an important quote as it not only fits the context of the show where so many characters have died, but it is also a piece of great advice for real people dealing with grief in their lives. Castiel also seems to be talking about his own reconciliation with the fact that one day he might have to see Sam and Dean die as they are mortals, while he is not.
Having A Winchester-Loving Heart
"I Won't Let Any Of You Die. And I Won't Let You Sacrifice Yourselves. You Mean Too Much To Me, To Everything".
In the season 12 episode, "First Blood," Castiel kills Billie to save Dean, Sam, and Mary. Once Dean confronts him about it, he passionately declares that he does not regret it and he cannot let any of the Winchesters die because they mean a lot to him and to the whole world.
The earnest emotions on Castiel's face in this scene are proof enough that he means every word. In fact, true to his word, a few episodes later, he is ready to die if it means sparing the lives of the Winchesters. Castiel has sacrificed himself numerous times for the Winchester family, especially Dean, and this time, he openly reveals their importance to him.
Learning To Be Human
"Now I Realize That There Is No Righteous Path. It's Just People Trying To Do Their Best In A World Where It's Far Too Easy To Do Your Worst".
Season 10, episode 9 sees Castiel being a fatherly figure to Claire Novak. Claire has hated Castiel for a long time, but Castiel has changed a lot since they last met. This episode reminds the viewers of this fact as his humanity is explored like never before.
This quote in the episode is a reflection of that as it demonstrates that Castiel has truly learned the human ways after being all these years on earth. It is also quite sad to realize that he actually learned it the hard way.
Reminding Dean What's Real
"Dean. You Asked, What About All Of This Is Real? We Are."
At the beginning of the final season, Team Free Will is going through a lot. They are at war against God himself, while recently having lost Mary and Jack. Dean is at his worst, as he feels like they had just been following God's plan all their life with no free will.
In season 15, episode 2, "Raising Hell," Cas reminds an agitated Dean that nothing may have been real Dean's entire life, but one thing he knows for sure is real is their relationship and their bond. This statement carries even more weight now in hindsight because, in the same season, Cas professes his love for Dean.
Tempting Fate
"You Don't Have To Be Ruled By Fate. You Can Choose Freedom. And I Still Believe That's Something Worth Fighting For".
Season 6 was the first time when Castiel took the center stage as the showrunners make him the villain at the end of the season. In the episode, "My Heart Will Go On," Castiel plays with Fate for his own ends when he orders Balthazar to 'unsink' the Titanic.
He says this quote to the Winchester brothers who have always rebelled against their fate. This signifies how much they have influenced him that he is no longer following orders but advocating free will. This Castiel quote can also inspire anyone who is struggling to choose between what they want and what others want for them.
Seeing Through Dean Like No One Else
"You Don't Think You Deserve To be Saved".
Castiel's introduction is one of the most pivotal moments in Supernatural, which occurred in season 4 episode 1, "Lazarus Rising". It changed the entire course of the show and gave a companion to Dean that he didn't know he needed.
The very first time Cas meets Dean, he is able to perceive the real Dean. Cas tells Dean blatantly that Dean doesn't think he deserved to be pulled out of Hell. It's so fascinating to see how easily Cas can sense his inner emotions and thoughts that he hardly ever reveals to anyone.
From Fighting For Heaven To Falling In Love With A Human
"You Changed Me, Dean."
The last scene of Castiel in Supernatural is also his most emotional moment. In episode 18 of season 15, Castiel confesses his love for Dean right before he is taken by the Empty. During the riveting confession speech, he opens his heart by telling Dean how much he means to him and how he changed him.
The entire speech is some of the best-written lines but the best one of them is "You changed me, Dean". Fans know this Castiel is not at all the same as when he was first introduced, but this sentence confirms that what changed him was Dean, the man he fell in love with. This proves that his love for Dean is epic because a mere mortal was able to instill human emotions and feelings into a celestial being from heaven.