Douglas J. Moo concisely summarizes the meaning of Romans 10:6–8 in the NLT Study Bible:

10:6-8 Here Paul quotes three phrases from Deut 30:12–14 dealing with the law, and he applies them to the Good News about Christ. We do not need to go up to heaven to find Christ (and thus to be made right with God), because God has already brought him down to earth as a man. Nor do we need to go down to the place of the dead to find Christ, because God has already raised him from the dead. To find Christ, we must simply believe in the message that is close at hand.