Albert Barnes Commentary 1 Samuel 6:7

"Now therefore take and prepare you a new cart, and two milch kine, on which there hath come no yoke; and tie the kine to the cart, and bring their calves home from them;" — 1 Samuel 6:7 (ASV)

A new cart ... cows on which no yoke has come - This was so ordered in reverence to the ark, and was a right and true feeling. See Mark 11:2 and Matthew 27:60. For the supposed special virtue of new things, see Judges 16:7 and Judges 16:11.