Charles Ellicott Commentary Jeremiah 31:37

"Thus saith Jehovah: If heaven above can be measured, and the foundations of the earth searched out beneath, then will I also cast off all the seed of Israel for all that they have done, saith Jehovah." — Jeremiah 31:37 (ASV)

If heaven above can be measured ... — The thought of the preceding verse is reproduced with a slight modification of meaning.

In addition to the idea, as stated above, that the stability of nature is a parable of the steadfastness of God’s laws and purposes in the spiritual world, there is an implied feeling, similar to that in Romans 11:33. This feeling is that humanity's finite intellect cannot fathom His ways of working out that purpose, any more than it can measure what, in the prophet’s mind, were the limitless heaven and the unfathomable earth.