Why is it important that in meiosis a cell copies the DNA once, but divides it twice?

Meiosis creates haploid cells. Meaning they only have one set of the chromosomes. So, in meiosis the DNA divides once, which would make two diploid cells. But then, the cell splits into two diploids, and again into four haploids. Gametes (reproductive cells) are always haploids. They have to be because each parent can only p on half of their genes.