Psalms 73:16

When I thought to know this - When I reviewed the history of our fathers, I saw that, though thou hadst from time to time hidden thy face because of their sins, yet thou hadst never utterly abandoned them to their adversaries; and it was not reasonable to conclude that thou wouldst do now what thou hadst never done before; and yet the continuance of our captivity, the oppressive hardships which we suffer, and the small prospect there is of release, puzzle me again. These things have been very painful to me.

When I thought to know this - When I endeavored to comprehend this, or to explain it to myself. The idea is that he "thought" on the subject, or "meditated" on it with a view to be able to understand it. He did not express his opinions and feelings to others, but he dwelt on them in his own mind; not to find additional difficulties, not to confirm himself in opposition to God, and not to find new occasions for distrusting the divine government, but to understand exactly how this was. It was his object to seek and understand "the truth."

It was too painful for me - Margin, "It was labor in mine eyes." The Hebrew word rendered "painful," means properly labor, toil, a burden; and the idea is, that the question was a burden - was too weighty for his weak powers.

73:16 To know - To find out the reason of this providence.