John Calvin Commentary Genesis 30:27

"And Laban said unto him, If now I have found favor in thine eyes, [tarry]: [for] I have divined that Jehovah hath blessed me for thy sake." — Genesis 30:27 (ASV)

I pray thee, if I have found favor in thine eyes. From this, we perceive that Jacob had not been a burdensome guest, since Laban soothes him with gentle words to obtain from him a longer period of service. For, greedy and grasping as he was, he would not have allowed Jacob to remain a moment in his house unless he had found his presence to be a sure source of profit.

Therefore, since he not only did not force him out but anxiously sought to keep him, we infer from this that the holy man had endured incredible labors. These labors had not only been enough for the support of a large family but had also brought great profit to his father-in-law. Therefore, he complains afterwards, not unjustly, that he had endured the heat of the day and the cold of the night.

Nevertheless, there is no doubt that God's blessing achieved more than any labors whatsoever, so that Laban perceived Jacob to be a source of great abundance, as he himself confesses. For he not only commends his faithfulness and diligence but also clearly states that he himself had been blessed by the Lord for Jacob’s sake.

It appears, then, that Laban's wealth had increased so much since Jacob's arrival that it was as if his profits had visibly come down from heaven. Moreover, since the Hebrew word נחש (nachash), among the Hebrews, means to know by omens or divination, some interpreters suppose that Laban, having been taught magical arts, discovered that Jacob's presence was beneficial and profitable to him.

Others, however, explain the words more simply, as meaning that he had confirmed it by experience. To me, the true interpretation seems to be as if he had said that God's blessing was as noticeable to him as if it had been confirmed by prophecy or discovered by divination.