John Calvin Commentary Ezekiel 1:7

"And their feet were straight feet; and the sole of their feet was like the sole of a calf`s foot; and they sparkled like burnished brass." — Ezekiel 1:7 (ASV)

This seems added as an explanation. Since Ezekiel has spoken of their human form, he adds that their feet were straight, although he calls them round or like those of a calf. I understand this straightness to refer not only to the feet but also to the legs. Therefore, it is as if he had said that these animals stood as humans do. For we differ from animals, which look down toward the ground. As the poet aptly remarks, when he praises the unique favor God has bestowed upon humanity,

Man looks aloft, and with erected eyes
Beholds his own hereditary skies.

The Prophet now signifies the same thing when he says that the animals had straight feet. He asserts that they had nothing similar to animals, but rather the appearance or likeness of a human. He says that their feet were round, and this seems to indicate their agility or the variety of their movements, as if he had said that their feet were not confined to any one direction, but wherever God impels them, they move easily, since their feet are round.

If any of us wishes to turn either to the right or the left, he will feel himself to be struggling against nature if he attempts at the same time to walk backward; if, however, his feet were round, or of the form of a calf’s foot, he could easily move in any direction.

This kind of agility, then, seems to be indicated in the animals. Regarding the sparks which shone like polished brass or steel, we know that this likeness often occurs in Scripture. For whenever God wishes to make His servants attentive, He presents new figures that may arouse their wonder. This very thing happened to our Prophet, because if the usual fleshly color had appeared in these animals, this perhaps would have been overlooked: the Prophet might not even have considered the meaning of the vision with sufficient attention.

But when he saw the glistening thighs and sparks shining in every direction, as if from polished steel, then he was compelled to consider this vision more attentively. Now, therefore, we see why he says that the appearance of the legs was like polished steel, and that sparks glittered on them.