Be knocking on heaven's door informal verb phrase
To say that someone is dying or approaching or very close to death.
Peter fought his disease bravely, but I'm afraid he's now knocking on heaven's door.
Can you come back home to meet our father, Mina? He is knocking on heaven's door.
To die or pass away
Used to refer to a place where everyone is happy or finds what they want
1. To pass away
2. To depart suddenly
1. One's success has gone down or ended.
2. One has passed away.
The verb "be" should be conjugated according to its tense.
Meaning absolutely certain or without a doubt
I am as sure as God made little green apples that Peter's the one for you, you two make a beautiful couple.