Bible references: 1 Timothy 6:16
One of the characteristics of man is death. Death cannot be bypassed by anyone. Everything existing on earth has a time whereby there existence elapses. The same thing is applicable to man. We all have a time that our existence here on earth will come to an end. Our mortal beings don't have the fortitude of living forever. It takes immortality to do so.
1 Timothy 6:16 - Who only hath immortality, dwelling in the light which no man can approach unto; whom no man hath seen, nor can see: to whom be honour and power everlasting. Amen.
God is the only being with the immortal nature. He's the only one who's existence can never be brought to an end. God meant for us to live like this originally, but due to the sin of our first parents, we were deprived of this chance.
But through the sacrifice of His son, we were given another chance. Our death is what reconnects man back to God for as many that are in Him.