This is a question Paul says not to ask: "Say not in thine heart." Barnes notes that asking who could go up to heaven "was used among the Jews, to denote any difficult undertaking." The worried heart thinks salvation must require an impossible feat, as if Christ had to be brought down from above. Barnes paraphrases Paul's warning: "Do not think, or suppose, that the doctrine is so difficult to be understood." Gill reads "Say not in thine heart" as "let not such a thought enter into thy mind, much less express it."

Paul answers inside the verse: asking that question would mean trying "to bring Christ down from above," but Christ has already come. He then rules out the opposite question about the deep (Romans 10:7) and gives the real answer: "The word is nigh thee, even in thy mouth, and in thy heart: that is, the word of faith, which we preach" (Romans 10:8). Whoever confesses "the Lord Jesus" and believes "that God hath raised him from the dead" "shall be saved" (Romans 10:9).

Paul is borrowing the words of Moses. Near the end of his life Moses told Israel that God's commandment "is not in heaven, that thou shouldest say, Who shall go up for us to heaven, and bring it unto us" (Deuteronomy 30:12). Barnes notes that Moses was urging obedience to commands that were plain and within reach, and that Paul does not claim Moses originally spoke of Christ; Paul uses Moses' language to describe the gospel. Gill likewise says the apostle uses some of Moses' phrases "with his own explications."

The question shows how near God has come. No one has to climb to heaven to find Christ, because God has already sent Him. Matthew Henry writes, "The way of justification and salvation has in it no such depths or knots as may discourage us."

This fits the whole passage. Israel went about "to establish their own righteousness" (Romans 10:3), as if salvation were a mountain to climb. The righteousness of faith answers that God has done the climbing down. What remains is to believe and confess (Romans 10:9-10).