It is strange terminology to those not familiar with the Old Testament Scriptures:
5 Moses writes this about the righteousness that is by the law: “The person who does these things will live by them.” 6 But the righteousness that is by faith says: “Do not say in your heart, ‘Who will ascend into heaven?’” (that is, to bring Christ down) 7 “or ‘Who will descend into the deep?’” (that is, to bring Christ up from the dead). 8 But what does it say? “The word is near you; it is in your mouth and in your heart,” that is, the message concerning faith that we proclaim.
This is actually a reference from Deuteronomy 30:11-14:
11 Now what I am commanding you today is not too difficult for you or beyond your reach. 12 It is not up in heaven, so that you have to ask, “Who will ascend into heaven to get it and proclaim it to us so we may obey it?” 13 Nor is it beyond the sea, so that you have to ask, “Who will cross the sea to get it and proclaim it to us so we may obey it?” 14 No, the word is very near you; it is in your mouth and in your heart so you may obey it.
In Deuteronomy, Moses is saying you don’t have to ascend to heaven to find what God requires, nor do you have to go to the distance sea. The Word is near you, in your mouth and heart so that you may obey it.
Paul is saying the same of Jesus. You don’t have to go to heaven to find Jesus. Or bring him up from the dead. He was incarnated and brought to this earth. He was resurrected and is no longer in the Abyss.
But what does it say? “The word is near you; it is in your mouth and in your heart,” that is, the message concerning faith that we proclaim.
We have Jesus in such a way that He is near us, in our mouths and in our hearts. He is not far from us. We can call on Him and have salvation.
You don’t have to go search the highest heavens or the deepest pits. Just call on him.