Cremation is permissible, but the Church does not recommend it because it does not bear full witness to the resurrection of the body as traditional earth burial does.
Whereas Platonists and other ideologies believe that only the soul can join God in Heaven, Catholics believe in the resurrection of both soul and body on the last day.
At the Second Vatican Council, the Catholic Church began to permit cremation, but traditional burial remains the strong preference because it bears a greater and more full witness to the dignity of the body. If we believe that Christ will resurrect our bodies when he comes again, it follows that we must appreciate and care for them in life and in death.
“The hope that we have of resurrection is preserved in the act of burial.”