در مسلخ عشق جز نکو را نکشند
In love slaughterhouse, they not kill except the good ones
روبه صفتان زشت خو را نکشند
They will not kill the ill-natured vulpines
گر عاشق صادقی ز کشتن مگریز
Do not run away from death if you are truthful in love
مردار بود هر آنکه او را نکشند
Anybody who is not killed in love slaughterhouse is a dead meat
In fact, the answer to your question is related to Rumi's mystical look.
If we look at it in a superficial way when a man is killed, apparently only a dead meat remains of him.
Everyone will eventually die.
The one killed in the slaughterhouse of love will be different from the one killed in the usual way.
The memory of the one who is killed in the way of love remains but The one who is killed in vain will not remain in remembrance and the one who doesn't stay in the memories is as dead meat.
You can watch a video (Puppet Opera Rumi) of this poem by Iranian singer Homayoun Shajarian here.
Watch the full video of this opera here
Also see something like this in Ghazal/Ode 636 from Rumi's Divan:
Go and die, go and die, In this Love, go and die. Once you've died in
this Love, You'd receive the spirit.
Go and die, go and die, Don't fear death, go and die. Go and leave
this dusty earth, Go fly up high into the sky.