John 1:48 - Matthew Poole's English Annotations on the Holy Bible

Nathanael wonders how Christ should know him, having not been of his familiar acquaintance. Christ tells him he saw him under the fig tree, before ever Philip called him. That was a very hot country, wherein people sought shadowy places; hence we read of sitting under their own vines and fig trees, Micah 4:4 Malachi 3:10; and it is likely that those being two luxuriant plants, that had large leaves, and ran out in long boughs, in hot weather they might under the covert of these plants not only sit as in an arbour to converse one with another, but also perform religious duties. Whether Christ saw him there eating and drinking, or conversing with friends, or reading, or praying, the Scripture saith not, and it is but vainly guessed; it is enough that by his telling this to him, he let him know that he saw him, though he was not in his view, and so was omnipresent and omniscient. Christ seeth us, where we are, and what we do, when we see not him; and he seeth our hearts, whether they be single or double, plain, or false and deceitful; which as in many cases it affords us much comfort, so it admonishes us to be at all times in the fear of the Lord.