A deeply religious retired teacher believed messages written on mirrors in her home were from God, telling her to change her will and leave her home to her young lover, a court has heard.
Benjamin Field, 28, used a white marker pen to leave biblical messages for 83-year-old Ann Moore-Martin as part of a campaign of "gaslighting".
Field - 57 years her junior - sent Miss Moore-Martin letters, postcards and poems speaking of his love and discussing marriage during a year-long seduction.
The church warden, who admits being in a fraudulent relationship with Miss Moore-Martin, also wrote messages urging her to give him £27,000 towards the cost of a dialysis machine, purportedly for his seriously ill brother Tom, 24.
Oxford Crown Court heard that Miss Moore-Martin, who never married or had children, later changed her will to leave her home in Maids Moreton, Buckinghamshire, to Field but changed her mind shortly before she died in May 2017 and alleged Field had poisoned her.
The jury was told Field had taken photographs of the messages, which were later recovered from his phone following his arrest.
The first message, illustrated with a cross, said: "All that you give him, He will return, Ten fold."
A second message said: "Your intentions are holy, Your work is not yet done, Take care and complete the task, Given to you by the Lord."
A third said: "Your soul will proceed directly to heaven, Her soul to joy; his to perfection, This good you will can never be undone. Peace is yours in me, your Lord. Amen."
A final message said: "Pray for Ben, Ben loves you."
The court heard that Miss Moore-Martin began to believe the messages were from God and Field also spoke of receiving them.
Oliver Saxby QC, prosecuting, previously told jurors that by the time she was receiving the messages Miss Moore-Martin had started feeling unwell and had started worrying about her sanity.
The court heard that Field wrote in his journal of living in Miss Moore-Martin's house after her death and that he would "lie in her bed as a widow". He later wrote of killing himself after her death.
Field had been introduced to her by her neighbour, university lecturer Peter Farquhar, 69, who Field was lodging with.
Field has admitted fraudulently beginning a relationship with Miss Moore-Martin as part of a plot to get her to change her will, but he denies conspiring with friend Martyn Smith, 32, to murder her.
Prosecutors allege Field targeted Miss Moore-Martin a few months after allegedly murdering Mr Farquhar.
He and Smith, a magician, are accused of plotting to make the church-going pensioner's death seem like an accident, such as dying during sex, falling down the stairs and choking on her dentures, or suicide having got her to change her will.
Field has admitted defrauding Miss Moore-Martin of £4,000 to buy a car and £27,000 to buy a dialysis machine. Tom Field and Smith deny having roles in the dialysis fraud.
It is claimed that Tom Field was seriously ill and needed the equipment to help him study at Cambridge University.
Field and Smith deny murder, conspiracy to murder and possession of an article for use in fraud.
Field, of Wellingborough Road, Olney, Buckinghamshire, also denies an alternative charge of attempted murder. He has admitted four charges of fraud and two of burglary.
Smith, of Penhalvean, Redruth, Cornwall, also denies two charges of fraud and one of burglary.
Tom Field, also of Wellingborough Road, Olney, denies a single charge of fraud.
The trial was adjourned until Wednesday.