Romans 10:6 - 7
ESV - 6 But the righteousness based on 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).
For follow-up discussion and general commentary on the topic. Comments are sorted chronologically.
The reason why we cannot say who will ascend or descend is because that is the judgment of God Almighty. To say otherwise would limit the grace of God on the lives of others. God says, not willing that any should perish but that all would come to repentance.