Grace’s revelations provide the first insight into Mugabe’s succession plans as he has kept the matter close to his chest.
They came a few hours after his wife heaped praise on Vice-President Emmerson Mnangagwa at a rally in his Midlands Province stronghold that led some to speculate she was on his side.
Grace is rumoured to belong to a faction known as G40 that is pushing for her ascendancy, or a compromise candidate once Mugabe decides to relinquish power.
She told thousands of Zanu PF supporters at a rally in Murewa that those who believed they were close to succeeding the 91-year-old leader were fooling themselves.
“God appoints leaders. That is why you see sometimes, even in the bible, young people were given power without even campaigning for it,” she thundered.
“People will look at you and judge. God will choose someone like Mugabe at the right time.
“If you listen to your wives who will be assuring you in the comfort of your homes, you are fooling yourselves.
“Listen to what the people are saying and if you choose to ignore that, it is your problem.”
She repeated her advice to Mugabe’s handpicked inner circle that includes vice-presidents Mnangagwa and Phelekezela Mphoko to remain grounded or risk the boot.
“Be good to people you meet on the way up because you will need them on your way down,” she warned.
“If Mugabe appoints you and people say they don’t want you, they will reject you. Don’t ride on other people’s backs; that will not work.”
Grace said no Zanu PF leader should try and build their profiles by claiming to be working with Mugabe, in another pointed rebuke of Mnangagwa.
“Others would say I was with him up and down the stairs but you will reap what you sow,” she retorted.
“You can’t sow seeds of despondency and reap joy. If we talk to you and you don’t listen, you will regret. Wait and remain loyal.”
Mnangagwa has in the past said he deserves his lofty post because he has worked with Mugabe for more than 50 years.
Grace said in the wake of Zanu PF divisions, the baton would be given to someone who did not belong to any faction.
She reiterated Mugabe would rule even from a wheelchair and even if he went blind.
“I said we will make a special wheelchair for Mugabe. We will push that wheelchair. Even if there is factionalism, mugoti unopiwa anyerere [reward will go to the quite one],” she said.
“If you get excited, people are vetting you. Many people are fanning factionalism but people in the grassroots are not fools.
“Don’t impose yourself. It has never worked and will never work. In future let’s learn to be people with good manners. Change your attitude!”
Grace accused three unnamed war veterans of fanning factionalism in the party.
War veterans have aligned themselves with Mnangagwa and have become a target of the First Lady’s acerbic attacks at her rallies.
On Saturday she said there was nothing special about war veterans.
“We are the same, those who went to war and those who did not,” she charged.
“We say no to the discrimination that you want to bring, you are causing divisions in the party.
“Real war veterans won’t say that. A person with discipline won’t say that nonsense. They must stop it forthwith,” Grace added.
“I will not be silenced. I am not afraid because you went to war. Some say I should not say this because I did not go to war.
“Two or three war veterans are doing that and they wanted to demonstrate against me. I said bring it on, you will find me ready.”
She also blasted those campaigning for her to be drafted into the presidium as VP ahead of the Zanu PF conference in Victoria Falls next month.
“We don’t want to confuse the electorate. There are people who are confusing others saying we are going to the conference and that they will choose me as VP,” she said.