The correct statement that explains the Pythagorean Theorem is:
If a triangle is a right triangle, then the sum of the squares of the legs is equal to the square of the hypotenuse.
In mathematical terms, if a right triangle has legs of lengths 'a' and 'b', and a hypotenuse of length 'c', the Pythagorean Theorem states that:
\[ a^2 + b^2 = c^2 \]