What does it mean that heaven says yes and the lower bound says yes?

Say a good word in heaven and bless everyone in the world. This is a couplet of Kitchen God, which describes the custom of Kitchen God.

For better or worse, I always hope that the kitchen god will put in a good word for me when he goes to heaven, so every year when he sacrifices to the kitchen god on the 23rd of the twelfth lunar month, a lot of honeydew melons will be offered to deal with the kitchen god. Kitchen God can't speak ill of people with honeydew melon on his mouth. What he has to say can only be sweet words. People also posted such a couplet next to his portrait:

Heaven speaks well;

The lower bound is auspicious.

Extended data:

Vulgarity of Kitchen God:

Grandma Chef lived in the Heavenly Palace for seven days, and everything was almost ready. On the night of the twelfth lunar month, she said goodbye to her parents and returned to earth with her husband on the fifth day of the first month. He and his wife gave things to the people, and everyone had a good year.

Since then, in order to commemorate the kindness of the kitchen god and his grandmother, people have painted them and pasted them in the kitchen. Every year on the 23rd day of the twelfth lunar month, they clean the house, offer sacrifices to the kitchen stove at night, and send the kitchen god and his grandmother back to the Heavenly Palace, so that they can "say good books in heaven and keep peace on earth".

In the Tang Dynasty, Lu Guimeng refuted the custom of offering sacrifices to stoves, saying, "The stove is broken, please build a new one. When it's done, please choose an auspicious day to tell us that the stove is in the ceremony and it's old. First of all, from cremation, people have the possibility of life and sacrifice. The speaker made a small accusation when he said that his god lived on earth. He also said that when he was a kitchen ghost, he recorded people's merits and demerits, and he would worship during the day and pray for good luck. This is close to what the alchemist said when Emperor Wu of the Han Dynasty. Confusing! "