What does the yellow sand in the Bible mean?

In the Bible, yellow sand is usually used as a symbol to imply difficulties, tests or challenges. For example, in the Old Testament, God promised Elijah that after he was saved in the flood, his descendants would be like "sand by the sea" (Genesis 22: 17). In the New Testament, Jesus also told his disciples that faith is like a grain of wheat. If you have faith, you can move this wheat grain to the mountain, even more than the yellow sand (Matthew 13:3 1-32). These quotations all emphasize the huge and uncountable figures represented by the yellow sand, as well as the firm belief and perseverance in the face of difficulties and obstacles.