"That's a pretty poor way to get out of an axplanation. I read it, but it's not an an answer. It explains nothing."
I think it helps to start with the "Flatland" concept. The two-dimensional characters in it are unable to grasp the three-dimensional world around them. Their two-dimensional minds just can't take in three dimensions.
God has dimensions that we don't. It seems to us contradictory that our choices could be meaningful if God already knows what we will choose, but that apparent contradiction is an artifact of our inability to comprehend those extra dimensions.
I don't understand it, either, but God has told us that He wants us to choose the good, and I don't think He would do that if the choices were meaningless.
As Aquinas said, "Some there are who presume so far on their wits that they think themselves capable of measuring the whole nature of things by their intellect, in that they esteem all things true which they see, and false which they see not. Accordingly, in order that man’s mind might be freed from this presumption, and seek the truth humbly, it was necessary that certain things far surpassing his intellect should be proposed to man by God."
Since you say we are incapable of grasping these concepts, why do you believe as you do?