誰言寸草心報得三春暉 is the last line of a famous poem. It is perceived as a tribute or ode to your parents or mother from a child or children that have left home.

The poem was written by Meng Jiao during the Tang Dynasty (about 1200 years ago). The Chinese title is “You Zi Yin” which means “The Traveler's Recite.”

The last line as shown here speaks of the generous and warm spring sunlight which gives the grass far beyond what the little grass can could ever give back (except perhaps by showing its lovely green leaves and flourishing). The metaphor is that the sun is your mother or parents, and you are the grass. Your parents raise you and give you all the love and care you need to prepare you for the world. A debt that you can never repay, nor is repayment expected.

The first part of the poem (not written in the characters to the left) suggests that the thread in a loving mother's hands is the shirt of her traveling offspring. Vigorously sewing while wishing them to come back sooner than they left.
...This part is really hard to translate into English that makes any sense but maybe you get the idea. We are talking about a poem that is so old that many Chinese people would have trouble reading it (as if it was the King James Version of Chinese).