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

The Judge appears 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

Judge Lexa appeared and Clarke said Lexa? Clarke ran over and hugged her tight and the Judge replied I’m not her, Clarke Clarke not letting go sobbed I know

Initially the Judge deemed humanity unworthy but Clarke and others proved her wrong and humanity was allowed to transcend except Clarke because she killed during the test

The Judge returned as Lexa just as Clarke said she didn’t want to be alone

Judge/Lexa startles Clarke you’re not

Clarke asks What do you want?

Lexa replies to explain

Clarke sighs There's no need. I get it. I bear it so they don't have to again.

Lexa compliments Such a curious species. You've added so much to us already. I'm glad to have been wrong about you.

Clarke for a moment feels hope Wait. Does that mean...you're here to take me with you?

Lexa frowns No. You can never join us, Clarke. Your actions must have a cost.

Clarke exclaims Just mine? Am I the only human being who ever sinned?

Lexa sympathetically answered Of course not, but you are the only test subject from any species anywhere in the universe since the dawn of time who committed murder during a test.

Clarke replied I’d do it again

Lexa smirked Madi knew you’d say that

Clarke said Madi’s with you then?

Lexa replies In a manner of speaking, yes. Her consciousness has joined ours. She's at peace. She'll never feel pain, she'll never die. She knew that living here without anyone her own age to love is something you wouldn't have wanted for her, even if it meant you being alone. I suppose that choice was made easier with the realization you wouldn't be.

Clarke looked confused Transcendence is a choice? You can choose to come back?

Lexa answers Of course. Though until now no one ever had.

Clarke peeks around the corner and sees her friends

Lexa states There won't be offspring, and they won't join us when they die. None of them seem to care.

Clarke acknowledges the Judge isn’t Lexa but still acts like the Judge is Lexa to some degree, even calling her Lexa and being physically affectionate. Clarke often exploits the Judge’s weakness to Lexa’s influence which resides in her despite not being Lexa herself. Clarke likes when the Judge has moments where she is taken over by the remnants of Lexa.

Clarke refuses to accept Lexa is gone, and that some part of Lexa isn’t in the Judge