subscribe vs receive

ViewController.swift

["hello world"]
  .publisher
  .subscribe(on: DispatchQueue.global(qos: .background)) // 1
  .map { string -> String in
    print("Is main thread in map:", Thread.isMainThread)
    return string
  }
  .breakpoint(receiveOutput: { str in
    print("current str:", str)
    return Thread.isMainThread // if main thread, breakpoint 
  })
  .print("debug")
  .receive(on: DispatchQueue.main) // 2
  .sink { str in
    print("Is main thread in sink:", Thread.isMainThread)
  }