Prosecutor Linda Allen asked jurors to use their heads, not their hearts, to determine LaShuan Harris' fate.
"I don't expect you to have a cold heart, but to have a rational mind," Allen said.
The mentally ill Oakland woman has pleaded not guilty to three counts of murder by reason of insanity.
Defense attorney Teresa Caffese said Harris believed completely that she was sending her children — 6-year-old Trayshun Harris, 2-year-old Taronta Greeley, Jr., and 16-month-old Joshoa Greeley — to heaven when she threw them over a railing and into the bay's cold waters. If Harris believed her delusions were real, Caffese argued, she is innocent of murder.
She said her client was, by many accounts, a good mother and gentle person whose lifelong struggle with mental illness finally overwhelmed her.
If the jury finds Harris guilty, it must then determine whether she was legally sane at the time of the crime. She faces a possible life prison sentence if convicted on all charges.
Caffese read from a letter she said Harris wrote from jail that was addressed to God.
"I did what you told me and now I am in lockup," Harris wrote. "Kiss my boys for me."
Allen said Harris deserves sympathy, but told jurors they could not use that as a factor in determining guilt or innocence.
While Harris believes she heard God's voice, it took a series of rational decisions to take her children from Oakland to the pier, undress the boys — one of whom struggled with her — hoist them over the railing and drop them into the water, Allen said.
"She knew you had to die to get to heaven. She knew how to get them to God. They had to die first, and that was her plan," she said.
The jury could begin deliberating Thursday.