The Judge is a transcended being that determines if a species is worthy of transcendence or if they should be annihilated, and then passes down their fate depending on the test subject's success or failure

Clarke was now a part of the test and she wasn’t prepared for memories of her dead girlfriend Lexa to be brought up.

Sometime later, long enough for Clarke to be annoyed by the Judge's absence, the Judge reappears as Lexa, knowing that Lexa was Clarke's greatest love.

The Judge however not only had access to Lexa’s form but her memories and personality as well, but to be fair the Judge had access to everyone’s memories including Lexa.

Clarke pauses and lovingly says Lexa?

Clarke then runs over and tightly hugs the Judge/Lexa to which the Judge/Lexa responds I’m not her, Clarke.

Clarke brokenly says I know

Clarke pulls away but not far The test isn’t over?

Judge/Lexa responds No. I'm sorry. We can't stop what's been set in motion. Your species must now be judged through you.

Judge/Lexa walks over to the pool of blood leftover from Cadogan's body This man was unarmed, no threat to you, yet you killed him. Why?

Clarke justifies herself He killed my daughter.

Lexa dismissively asks Is Madi dead?

Clarke defensively replied No, but she will be because of him.

Lexa criticizes So your need for revenge is more important than the fate of the entire human race?

Clarke defensively replied It's not revenge. It's justice.

Lexa speaks Clarke

Lexa says in Trigedasleng A rose by any other name is still...blood must have blood.

Clarke snapped You don’t know my pain!

Lexa counters You're wrong. During the test, I sense every part of you. I'm feeling your pain right now.

Clarke argues Really? Then feel me holding Lexa as she dies. Feel me seeing someone else wear my Mother's face. Feel me murder my best friend to save my child, only to have her die anyway. Feel that!

Lexa judgmentally replies You suffer and inflict suffering on others. Pain begets pain. That's not justice, Clarke. You say you do these things to protect your people, but you're all one...people. That much Cadogan had right.

Clarke gets frustrated with the self righteous Judge especially since they are without consent using Lexa’s form, they were using Lexa’s words against her, Clarke hated that it wasn’t Lexa yet acted somewhat like Lexa, Clarke hated that she despite hating the Judge’s stance wanted the Judge to keep Lexa’s form just so she could be with Lexa in some form

Clarke finally replies He created a world without love to get to you. He killed my child to get to you. Have you ever considered that you're the problem? How dare you judge me when you annihilate entire species because they don't live up to your ideals? Have I pulled the lever to commit genocide? Yes, I have. And did love make me do this? You're damn right it did! But what's your excuse? You play games with people and call yourselves higher beings. You are no better than the murderers I've killed, and you are no better than me!

Lexa seemed detached and unaffected as she coldly replied I am sorry for all you have lost. You've borne so much...but if you are humanity, then I'm afraid humanity is not worthy of taking the next step. It has been decided.

Lexa twists the knife further as she speaks in Trigedasleng and quotes the real Lexa Your fight is over

Clarke yelled Lexa would never do this! You wear her face but you don’t have her soul! You act like you know me, like you know her, like you know love, but you’ll never understand! You could never! If you remotely understood you wouldn’t use Lexa’s form to torture me you sadistic sociopath! I loved her and you mock her and you judge me and you take what I love and you force me to remember her face as yours! Lexa would never wipe out an entire race based off a portion’s behavior!

Lexa responded I told you I’m not her

Clarke emotionally replies Yet you carry everything she was within you, all her memories, all her mannerisms, the way she talks, walks!