I don't know if it's ever been brought up here before. Having watched Messi for years, I noticed that Messi is able to hit the ball at perfect precision and to generate enormous power from it when the ball is moving. His first touch, passing and shooting all are perfectly executed which requires the ball being hit at the right time and right place. Hence, combined his vision and awareness, he is easily the best player that I have seen for open play football.
When the ball is still that is another story. He seems not be able to match that precision and power generated when the ball is moving. This could be the reason behind his relatively low conversion rates of freekicks and penalties. My only conclusion is that Messi, given his body height and weight or body mass, is not a naturally powerful hitter of the ball. So when the ball is still, he needs to hit it harder to create more power. But when he hits it harder, that inevitably affects the precise spot he wants to hit the ball.
However, when the ball is moving, he just knows exactly where the sweet spot is on the ball and hits it millimetre perfect, which drives the initial kinetic energy of the ball to the way he wants while optimizing the power generated. When you think of that, you just know how incredible Messi feels the ball. That's why we always say the ball is part of his body. So while I admit the fact that Messi is not the best penalty and freekick taker, this just magnifies how gifted he is on the ball.