Before I respond, I think De Maria's objection makes perfect sense, given his Roman Catholic perspective.
The Catholic perspective is not the one you described. I have corrected your straw man and provided the true Catholic perspective.
And to complicate matters for the Reformed position, I must admit at the outset that I am unaware of any passage that specifically says "God died only for the elect." That said, what follows is a response to both De Maria's take onRomans 5:6 and De Maria's request for a passage that teaches that God died for the elect. Let's first begin with Romans 5:6
Romans 5:6 in Context
The problem is your presupposition. You start from the erroneous premise that Jesus died only for the elect. Therefore, when St. Paul says, "He died for US…" you read into it that He "only" died for those of us who chose to accept His sacrifice. But Rom 5:6 is the correction to that error in case anyone were to fall into it.
St. Paul says, "He died for US…" But in Rom 5:6, he clarifies that Jesus died for the ungodly. That means Jesus died for all creation. He died for the world. He died for us because He died for all. We are not excluded when we way He died for all. We are included in that number. We are a subset of that number.
Let's look at Rom 5:1-11 in context. First, St. Paul is contrasting the Jews and the Gentiles. He is showing how the Gentiles are now grafted into the tree and are savable. Because Jews thought that God would not save Gentiles.
So, we begin where he says:
Therefore, since we have been justified by faith, we have peace with God through our Lord Jesus Christ. 2 Through him we have also obtained access by faith 2 into this grace in which we stand, and we rejoice in hope of the glory of God.
We, in this verse is a reference to Catholics. Although not yet called Catholics, it is Catholics who are justified by faith through the Sacraments. And that is what St. Paul is talking about. We who are justified by faith through the Sacraments.
3 Not only that, but we rejoice in our sufferings, knowing that suffering produces endurance, 4 and endurance produces character, and character produces hope, 5 and hope does not put us to shame, because God's love has been poured into our hearts through the Holy Spirit who has been given to us.
Here he mentions suffering which is an essential part of salvation. Unless we suffer with Christ, we will not be saved with Him:
Romans 8:17
And if children, then heirs; heirs of God, and joint-heirs with Christ; if so be that we suffer with him, that we may be also glorified together.
6 For while we were still weak, at the right time Christ died for the ungodly.
Here is the correction. While we were still weak. The we refers to those who prior to Christ's sacrifice were still sinners.
Note that He didn't say, "while we were still weak, Christ died for US." Why not say it. He had used that pronoun approximately 13 times in the past 11 sentences. But that is not what he means. He means exactly what the verse says. While we were sinners, weak in the flesh, Christ died for all who are not God. Christ died for all who are not divine. Christ died for the whole world. Christ died for all.
Therefore, Christ died for us because He died for all.
7 For one will scarcely die for a righteous person—though perhaps for a good person one would dare even to die—8 but God shows his love for us in that while we were still sinners, Christ died for us.
Then, St. Paul refocuses on those who have repented and accepted God's call. But that is not a denial of the fact that Jesus died for all.
9 Since, therefore, we have now been justified by his blood, much more shall we be saved by him from the wrath of God.
This is a reference to the Mass and the original Passover, where God passed over the Hebrews who had marked their door post with the blood of the lamb.
Christ is now our Passover and we are justified in His Blood when we drink of the Cup of Salvation. And when we drink of His Blood, we are saved from God's anger.
10 For if while we were enemies we were reconciled to God by the death of his Son, much more, now that we are reconciled, shall we be saved by his life.
This is still a reference to the Eucharist.
While we were dead in our sins, Jesus died for us in order that we might be reconciled to God. Now that we are reconciled to God, Jesus saves us by His life. His Blood that He shed for us on the Cross, is in the Holy Eucharist and is our life. If we partake of it.
11 More than that, we also rejoice in God through our Lord Jesus Christ, through whom we have now received reconciliation (Romans 5:1-11, ESV).
Furthermore, still talking about those who live according to the Catholic Faith, we now rejoice because God offers us forgiveness in the Sacrament of Reconciliation.
So, we begin where he says:
Therefore, since we have been justified by faith, we have peace with God through our Lord Jesus Christ. 2 Through him we have also obtained access by faith 2 into this grace in which we stand, and we rejoice in hope of the glory of God.
We, in this verse is a reference to Catholics. Although not yet called Catholics, it is Catholics who are justified by faith through the Sacraments. And that is what St. Paul is talking about. We who are justified by faith through the Sacraments.
3 Not only that, but we rejoice in our sufferings, knowing that suffering produces endurance, 4 and endurance produces character, and character produces hope, 5 and hope does not put us to shame, because God's love has been poured into our hearts through the Holy Spirit who has been given to us.
Here he mentions suffering which is an essential part of salvation. Unless we suffer with Christ, we will not be saved with Him:
Romans 8:17
And if children, then heirs; heirs of God, and joint-heirs with Christ; if so be that we suffer with him, that we may be also glorified together.
6 For while we were still weak, at the right time Christ died for the ungodly.
Here is the correction. While we were still weak. The we refers to those who prior to Christ's sacrifice were still sinners.
Note that He didn't say, "while we were still weak, Christ died for US." Why not say it. He had used that pronoun approximately 13 times in the past 11 sentences. But that is not what he means. He means exactly what the verse says. While we were sinners, weak in the flesh, Christ died for all who are not God. Christ died for all who are not divine. Christ died for the whole world. Christ died for all.
Therefore, Christ died for us because He died for all.
7 For one will scarcely die for a righteous person—though perhaps for a good person one would dare even to die—8 but God shows his love for us in that while we were still sinners, Christ died for us.
Then, St. Paul refocuses on those who have repented and accepted God's call. But that is not a denial of the fact that Jesus died for all.
9 Since, therefore, we have now been justified by his blood, much more shall we be saved by him from the wrath of God.
This is a reference to the Mass and the original Passover, where God passed over the Hebrews who had marked their door post with the blood of the lamb.
Christ is now our Passover and we are justified in His Blood when we drink of the Cup of Salvation. And when we drink of His Blood, we are saved from God's anger.
10 For if while we were enemies we were reconciled to God by the death of his Son, much more, now that we are reconciled, shall we be saved by his life.
This is still a reference to the Eucharist.
While we were dead in our sins, Jesus died for us in order that we might be reconciled to God. Now that we are reconciled to God, Jesus saves us by His life. His Blood that He shed for us on the Cross, is in the Holy Eucharist and is our life. If we partake of it.
11 More than that, we also rejoice in God through our Lord Jesus Christ, through whom we have now received reconciliation (Romans 5:1-11, ESV).
Furthermore, still talking about those who live according to the Catholic Faith, we now rejoice because God offers us forgiveness in the Sacrament of Reconciliation.
Sincerely,
De Maria