Why should we use interface in MVP pattern for Android?

I'm making an Android app using Kotlin for the first time using MVP pattern. My questions is, why do I need interfaces for View and Presenter as Kotlin provides higher order functions? Can't we just communicate using those higher order functions? Is the use of pattern without interfaces bad?

I have looked and read lots of article and tutorials but non answered my question. Is what I am doing in the code below a wrong practice? Can someone explain it to me?

In my Activity

override fun init() {

    btn_login.setOnClickListener {
        LoginPresenter.userLogin(et_emailAddress.text.toString(),et_password.text.toString()){
            if (it){
                //do something
            }else{
                //do something
            }
        }
    }
}

My Presenter

object LoginPresenter {

fun userLogin(emailId: String, password: String, completion: (Boolean) -> Unit) {
    //do something
    completion(true)
 }
}