What does "a reed across the river" mean? What is commonly used to describe?

According to the legend of crossing a river by a reed, Dharma is the third son of King Tianzhu Xiang. Prajna Paramita, the 27th Buddha, worshiped Sakyamuni's disciple since childhood. One day, Dharma asked his master for advice and said, "Where should I spread Buddhism after I get it?" Prajna paramita said, "You are going to Sinian (that is, China)". He also said: "After the Sinian, don't live in the south, where the monarch likes political achievements and doesn't understand Buddhism." According to Master's instructions, Dharma packed his bags and sailed across the ocean in a gondola. It took him three years to come to China. After Dharma arrived in China, Guangzhou secretariat learned about this matter and quickly reported it to Jinling. Wu Liang and Xiang Yan immediately sent messengers with Dharma to Nanjing to welcome him and entertain his guests. Emperor Wu is a Buddhist and advocates self-liberation. Dharma is a Zen Mahayana school, which advocates sitting by the wall and benefiting all beings. Because of different views, every time I talk about Buddhism, I always don't speculate. At this time, Dharma felt that Nanjing was not a place to stay for a long time, so he left Xiao Yan and crossed the river to the north. There is a monk named Shen Guang in China, who is from Xingyang, Henan. At that time, Shen Guang gave a lecture in Yuhuatai, Nanjing. The local people said: "Shen Guang gave a lecture euphemistically and sweetly, and the golden lotus was born on the ground, and the stubborn stone nodded." The people who watched the lecture were packed three floors away. Dharma left Liang Wudi for the north and passed by Yuhuatai. When he saw Shen Guang preaching there, he squeezed into the crowd and listened attentively. When Dharma was listening, he heard some nodding and some shaking his head. Nodding your head means you agree with Shen Guang, shaking your head means you disagree with Shen Guang. In the process of explanation, Shen Guang found that Dharma shook his head and thought it was the biggest disrespect for himself. He asked Dharma, "Why are you shaking your head?" Because of his different views on Buddhism, Dharma gave in and left Yuhuatai to cross the river to the north. After Dharma left, someone in the audience said to Shen Guang, "Do you know who that man was just now? He is the Indian monk bodhidharma, who is proficient in Buddhism and knowledgeable. " Hearing this, Shen Guang felt very ashamed. When master came, he was rude just now. So I quickly chased dharma to apologize. Dharma walked ahead, followed by Shen Guang, until you reached the bank of the Yangtze River. Dharma is in a hurry to cross the river and stop at the bank. There is no bridge, no boat or even a figure on the vast sea. How can we cross the river here? Dharma is in a hurry. Who knows "God never shuts one door but he opens another"? At this helpless moment, Dharma suddenly found an old lady sitting not far from the shore, with a bundle of reeds beside her, as if waiting for the boat to cross the river. Dharma thought to himself, if he is old, why is he alone without an escort? Let it be! Had to ask her father for help. So he stepped forward and respectfully bowed to the old man and said, "Old Bodhisattva, I want to cross the river, but there is no boat. Please give me a reed so that I can walk instead of walking. " The old man raised his head and studied Buddhism carefully. I saw his eyes protruding, a full face of beard, curly, burly, calm, strong image and extraordinary appearance. The old man nodded secretly and took out a reed and an instrument. Dharma took the reed in both hands, thanked the old man and left. When he got to the river, he put the reed by the river, only to see a reed flower with its head held high and five reed leaves unfolded. Dharma treads on reeds and crosses the Yangtze River. Regardless of fatigue, Shen Guang chased Dharma to the river. When he saw Dharma crossing the river with a reed, he angrily ran to the old man's side. Without asking indiscriminately, he picked up a bundle of reeds beside the old man, plopped it into the water, jumped on the bundle of reeds and hurried across the river. Strangely, this bundle of reeds did not advance, but quickly sank into the water. Seeing that the situation was not good, Shenguang waded out in a hurry and almost drowned. Shen Guang rushed to the muddy old man and listened gently to the rebuke: "Give him a reed and you will cross the river. Why can't I give you a bundle of reeds? " The old man answered unhurriedly: "He is my reed, helping others;" You are the reed that robbed me. Everything has a destiny. Can you help me for no reason? " The old man said, "In a blink of an eye, there was no one over the vast river. At this moment, Shen Guang knew what he had lost, and he sighed in shame. He called the weather ineffective, and he shouldn't call the ground. He was very sad and regretted it. After Dharma crossed the river, he walked with a mord in his hand, worshiped on the mountain and meditated in the temple. In the third year of Xiaochang in the Northern Wei Dynasty (AD 527), he arrived at Shaolin Temple in Songshan Mountain. Dharma saw here surrounded by mountains, dense forests, beautiful scenery, quiet environment, prosperous Buddhism and love affairs. I think this is really a rare pure land of Buddhism. So he used Shaolin Temple as a missionary Dojo. Widely accept monks and disciples, preach Zen for the first time. Since then, Dharma has become the ancestor of Zen in China, and Shaolin Temple is called the ancestral home of Zen in China. Now there are statues of statues and reeds crossing the river in the stele gallery of Shaolin Temple. The ancients had a poem praising the sun: meet again after passing the water and cross the river sadly alone. The sun is pitiful, just like two horses, singing softly.