I would answer that paragraph differently.
On the cross, He said, “It is finished” (John 19:30 in Gospel of John). What was finished? The sacrifice. The Lamb had been offered. Just as in the sanctuary, the victim was slain once. There is no repeated sacrifice. In that sense, the atoning offering was complete. But does Scripture show that everything in the plan of salvation was completed at that moment? YES.
Jesus also said, “He that endureth to the end, the same shall be saved” (Matthew 24:13). If the whole plan was finished for every person at the cross, why speak of enduring to the end?
He said, “The word that I spake, the same shall judge him in the last day” (John 12:48). That judgment was still future. Even after the cross, there is a last day.
Look at His prayer in John 17. Before the cross He said, “I glorified thee on the earth, having accomplished the work which thou hast given me to do” (John 17:4). Yet He had not even died yet. So “finished” does not mean every part of God’s plan through all time was fully carried out. It means the specific task at that moment was completed.
On the cross, the sacrifice was finished. The offering was complete. But salvation also includes resurrection, ascension, intercession, the preaching of the gospel to all nations, the judgment, and the final kingdom. Jesus spoke of sitting on His throne in glory and judging the nations (Matthew 25:31–32). That clearly was not finished at Calvary.
The sacrifice was finished. The Lamb was offered once for all. Nothing can be added to His blood.
But the application of that sacrifice to each person, the call to repent, to believe, to endure, the future judgment, and the bringing in of the kingdom were not finished at that moment.
The cross is the foundation. It is complete. But the full plan of salvation, as Jesus Himself described it, unfolds from the cross until the last day.
Sorry to burst your bubble