C. F. Keil and Franz Delitzsch on Exodus 9:29-30

Exo 9:29-30

Moses promised that his request should be granted, that he might know “that the land belonged to Jehovah,” i.e., that Jehovah ruled as Lord over Egypt (cf. Exo 8:18); at the same time he told him that the fear manifested by himself and his servants was no true fear of God. יי מפּני ירא denotes the true fear of God, which includes a voluntary subjection to the divine will. Observe the expression, Jehovah, Elohim: Jehovah, who is Elohim, the Being to be honoured as supreme, the true God.