Circle any number in the matrix, for example, $608$ as below. Draw a line through all the squares that lie in the same row and column as your selected number.
Circle another number which has not got a line through it, for example, $343$ and again rule out all squares in the same row and column.
Repeat for a third time, then circle the remaining number which has not got a line through it.
Add all the circled numbers together. Note your answer.
Try again with a different starting number. What do you notice?
See if you can work out how this matrix works.
Below is a simpler one which might be easier to investigate.
Can you make a similar matrix which generates a different total?