That verse scares the living shit out of me too, for few reasons. Like Jesus said "if you love me, you will keep my commandments" and His commandments were to love everyone and to save their souls. I dont even love myself or take care of myself and my social anxiety makes it impossible for me to spread the Word.
But again, its written that we will be saved by grace through faith alone, thats why He went on the cross, that whoever believes will be saved.
When He talked about those who healed the sick, cast out the demons and prophesized in His name, imo He meant on people like Judas or modern prosperity preachers, who never believed, never put faith in Jesus for salvation. They did it only for money and benefits. Thats why He said "I NEVER knew you" If they believed faithfully at some point he wouldnt say never knew you.