John Calvin Commentary John 1:48

"Nathanael saith unto him, Whence knowest thou me? Jesus answered and said unto him, Before Philip called thee, when thou wast under the fig tree, I saw thee." — John 1:48 (ASV)

From where do you know? Though Christ did not intend to flatter him, yet he wished to be heard by him, to draw forth a new question by the reply to which he would prove himself to be the Son of God. Nor is it without a good reason that Nathanael asks from where Christ knew him; for to meet with a man of such uprightness as to be free from all deceit is an uncommon case, and to know such purity of heart belongs to God alone.

The reply of Christ, however, appears to be inappropriate. For though he saw Nathanael under the fig-tree, it does not follow from this that he could penetrate into the deep secrets of the heart.

But there is another reason. As it belongs to God to know men when they are not seen, so also does it belong to Him to see what is not visible to the eyes. Since Nathanael knew that Christ did not see him as humans do, but by a look truly divine, this might have led him to conclude that Christ was not now speaking as a man. The proof, therefore, is taken from things which are of the same class, for it no less belongs to God to see what lies beyond our view than to judge concerning purity of heart.

We ought also to gather from this passage a useful doctrine: when we are not thinking of Christ, we are observed by him. And it is necessary that this should be so, that he may bring us back when we have wandered from the right path.