Ha, ha, "dead" can mean different things. There are some people we might call "living" since their physical bodies are moving around, but spiritually they are dead. . . .
Matthew 8:21 And another of his disciples said unto him, Lord, suffer me first to go and bury my father.
22 But Jesus said unto him, Follow me; and let the dead bury their dead.
Some could say Jesus was stark raving mad when he said what he did in the passage Marks quoted for us.
John 11
23 Jesus saith unto her, Thy brother shall rise again.
24 Martha saith unto him, I know that he shall rise again in the resurrection at the last day.
25 Jesus said unto her, I am the resurrection, and the life: he that believeth in me, though he were dead, yet shall he live:
26 And whosoever liveth and believeth in me shall never die. Believest thou this?
27 She saith unto him, Yea, Lord: I believe that thou art the Christ, the Son of God, which should come into the world.
Obviously -- obviously, he wasn't talking about physical bodies.
I had a dear aunt who held different beliefs than I did; but she was a wonderful person. I had a conversation with her shortly before she "died." She said she was ready to go. That gave me comfort; but I got an even bigger surprise on night when I was caught up in the spirit and met her.
She was with three other people who didn't notice me. I said stupidly, "I thought you were dead." She laughed -- and it was her laugh -- I've never met another person who laughed the same way. Then she said, "Some people might call it that." Then she indicated that I shouldn't linger. If we kept talking, we might bother the other people with her. That made sense to me.
I have met other "dead" people. No, I don't go out looking for them -- I wouldn't want to disturb their rest or interfere with them in any way; but if they turn up, they turn up. I've met my Mother and Father after they passed; and I've met Abraham and Sarah. Assuredly -- I guarantee it that Jesus was right -- Abraham is alive. God is the God of the living.
What is sad is when the "dead" people in living physical bodies do not find God in this lifetime on earth. When their physical bodies die, they remain spiritually dead. Some enter a state you could compare to sleeping. This type of "dead" person knows nothing. God knows how to wake them up -- it sounds like a trumpet to some people. Ha, and some saints can also hear the same trumpet before their physical bodies die. Moses did. John did. If you are ready to hear it and not afraid of it -- it changes you now. You do not need to go to sleep to be awakened later.