Yes, of course, God is omnipresent. But this is spoken of not only in biblical revelation...
Yes, of course, God is omnipresent. But this is spoken of not only in biblical revelation; pantheistic religions are very ancient. But the God to whom the psalmist turns has astonishing differences from the god of pantheistic religions: He is Spirit, but He has a face turned toward me and a hand with which He leads and holds me. God has personal relationships with me, relationships that are not broken on His side even when I avoid them. And one more thing: to descend into the underworld means to die, to go away from God forever, into nonbeing. But God comes even there, in order to bring even nonbeing into being.
138 David praises God for his goodness, and foretells that other kings will praise him, Psa 138:1-5. He rejoices in hope of still greater blessings, Psa 138:6-8. A psalm of David.