You said;
I asked why Jesus would speak to his disciples about his return when they didn't even understand that he had to go away.
In fact I got that wrong; Jesus wasn't speaking to his disciples here, but to the Jewish leaders who were questioning his authority. If we read these verses in context, John 5:21 says that just as the Father gives life to the dead, so the Son gives life to those he chooses. John 5:25 says, "truly I tell you a time is coming and has now come when the dead will hear the voice of the Son of God". (Tradition says that before Jesus was raised from the dead, he went and preached to all who had died before they had been able to hear the Gospel.) He then goes on to say that whoever hears the voice of the Son of God will live.
Then he told them that a time was coming when all who were in their graves would hear his voice and come out. He says nothing here about his return. It was you who said that people coming out of their graves had to indicate the 2nd coming.
In fact, the dead hearing his voice could refer to when Jesus preached to them after his own death, or it could be that they heard the Gospel after the tombs were opened at his crucifixion.
I wasn't talking about Jesus' return. I was challenging your assumption about John 5:28.
That was my only point.
John 5:28-29 says;
Where, in those verses, are the words, "when I return"? And Jesus has been talking about the Father, do the words, "his voice" mean the voice of God the Father, or the voice of Jesus, the Son of God?
Jesus might have been hinting at future judgement and how even the dead who have rejected the Gospel will be judged and condemned. But he says nothing about his return - he hadn't even yet mentioned going away, never mind coming back again. The subject of the passage is the authority of the Son, because the Jewish leaders were grumbling that Jesus healed on the sabbath.