Did Jesus Christ come down from heaven to die of his own will, according to John 6:28?

No. He came to do his Father's will.

Jesus’ self-sacrificing course of action clearly showed his purpose, or design.

He was not leading a superficial life, just seeking pleasure and fun.

He knew that he had not given up his former life in heaven in order to waste away a few years on earth in selfish pursuits.

he stated: “I have come down from heaven to do, not my will, but the will of him that sent me.” John 6:38

Jesus was single-minded in his devotion to his Father’s cause, always putting it above his own will, even down to an ignominious death.

It was God's will that anyone who wants to sit in the position of System Sovereign as a Son of God they have to fulfill Seven Bestowals. This was Jesus' Seventh Bestowal. He had to do this if He wanted to be in that spot.

it's God's will Jehovah Witnesses become christians

Timothy 3:16..all scripture is inspired...which is another way of saying that it is a load of total bollocks.