It is usually used to explain the five-element balance of individual birthdates. The core tablet of life here refers to the heavenly stems and earthly branches combination indicating the year of birth, the lack of soil refers to the lack of soil elements in the five elements, the horse refers to the earthly branch with horses in the life, and the heavy soil in the plate means that there are more soil elements in the eight characters.
It should be noted that these terms are only a symbol and form of numerology. Don't trust and rely too much, and treat fate and life rationally.