Deuteronomy 30:12
10 if you obey the Lord your God and keep his commandments and statutes that are written in this scroll of the law. But you must turn to him with your whole mind and being. 11 “This commandment I am giving you today is not too difficult for you, nor is it too remote. 12 It is not in heaven, as though one must say, ‘Who will go up to heaven to get it for us and proclaim it to us so we may obey it?’ 13 And it is not across the sea, as though one must say, ‘Who will cross over to the other side of the sea and get it for us and proclaim it to us so we may obey it?’ 14 For the thing is very near you—it is in your mouth and in your mind so that you can do it.
Romans 10:6
4 For Christ is the end of the law, with the result that there is righteousness for everyone who believes. 5 For Moses writes about the righteousness that is by the law: “The one 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 abyss?” (that is, to bring Christ up from the dead). 8 But what does it say? “The word is near you, in your mouth and in your heart” (that is, the word of faith that we preach),
Notes and References
"... It is in the exposition of Psalm 68:18 that a horizontal barrier is possibly implied. This is the barrier between “the lower parts of the earth” and the upper world, “far above all the heavens”, which Christ broke when he ascended. But if it is implied, no particular stress is laid on it. On the verb “ascended” in the Psalm the comment is made ... In this exposition the crucial question is whether by “the lower parts of the earth” the earth itself is indicated (as being “lower” in relation to the world above), or the underworld (as being “lower” in relation to the earth). It is not possible to reach complete certainty. Comparison with Romans 10:6, where (in a pesher exegesis of Deuteronomy 30:12–14) ascending into heaven is contrasted with descending into the abyss, suggests the latter interpretation; comparison with John 3:13 (and the Gospel of John has special affinities with the Epistle to the Ephesians) suggests the former, for in John 3:13 the Son of Man’s ascent into heaven is paralleled by his coming down from heaven (that is, to earth) ..."
Bruce, F. F. Paul, Apostle of the Heart Set Free (pp. 493-494) Paternoster, 1977