Meiosis effectively halves the number of chromosomes in a cell. In our cells, we have pairs of chromosomes. These cells are called diploid. Meiosis results in cells that have only one chromosome from each pair, creating haploid cells. Mitosis makes an exact genetic copy of a cell. So, when a human cell divides by mitosis, it creates 2 identical cells with pairs of chromosomes.
During fertilization of an egg cell with a sperm cell, each cell contributes half the necessary genetic material (haploid), so the resulting zygote once again has pairs of chromosomes (diploid). If egg and sperm cells were created by mitosis, each cell would have pairs of chromosomes, and the resulting zygote would be tetraploid (4 of each chromsome) ! A typical chromosome number for humans is 23 pairs (46 total). If two diploid cells united during fertilization, the result would be a cell with so many chromosomes that it could not be human and would not survive.
If all cells in your body divided by meiosis, each time you made new skin cells, they would have fewer and fewer chromosomes. Again, changing the number of chromosomes is not supportive of survival.