The psychiatrist, an expert witness for the defence, said Tarapata was "obsessed with the Bible" and was receiving messages from it as well as number plates.
He said Tarapata, who the doctor assessed months after the killings, was "consumed" and also hearing the "voice of God talking to him and commanding him to do things".
"It's my understanding that in the time period leading up to the homicides that [Tarapata] was psychotic, he was paranoid, he feared for his safety, he feared for the safety of his partner," he said.
"He was communicating with God through reading the Bible and making his sacrifices."
Tarapata was known to be making daily sacrifices to a higher being, often by burning meat as a gift to God, the court has heard.
"I believe he also held the delusional belief that his partner was having some kind of inappropriate sexual relationship," Skipworth said.
Skipworth said a day or so before the killings, Tarapata was "commanded by God" to kill Matthews and Fanning.
"He questioned God about whether he needed to kill them ... He was told he did need to kill them for their sins against his partner," the doctor said.
Skipworth said he believed Tarapata saw God as the "highest [moral] authority that there was" and after the stabbings immediately reverted to the Bible "to see what he should do".
Prior to the development of his diagnosed schizophrenia Tarapata had shown no signs he was religious, Skipworth said.
"He nonetheless meets the test of insanity", Skipworth said, adding Tarapata did know his actions were morally wrong.
Skipworth accepted that those who have schizophrenia could still accept the morality of their actions.
Under cross-examination by Crown prosecutor Richard Marchant, Skipworth said despite the "frenzied attack" and the "fact he lied" about what he did, Tarapata believed there was no greater authority than God.
The doctor accepted that Tarapata showed some awareness for the legality of his actions but he "didn't regard them as being morally wrong because he was conducted to do so by God".
Tarapata washed his hands, clothes, and seemingly made efforts to discard the knife after the attack before being arrested in Huntly at about midnight that day.
Skipworth said Tarapata has not responded well to antipsychotic medication during medical trials.
The psychiatrist's evidence is in direct contradiction to the Crown's expert psychiatrist, who said Tarapata knew what he was doing was morally wrong.
Moments before the killings Tarapata arrived at the pawn shop with his partner, Tamara Cassie, and their children.
Cassie, who also worked part-time at the store, entered the Great South Rd store and told Tarapata to stay in the car with her children, the court heard earlier in the trial.
Matthews and Fanning, the owner of the shop, were sitting in the lunchroom at the back of the shop eating noodles.
But Tarapata left the car and snuck around to the rear of the business.
He then stabbed them to death over about three minutes.
Fanning was stabbed six times to his chest and neck, and Matthews was stabbed 15 times. His throat was cut.
The trial continues.
