I have addressed John 19:30 and τετελεσται in a few articles, including this response to Dave Bartosiewicz.
In his commentary on John 19:30, John Calvin (1509-1564) offered the following, showing that Calvin did not believe that “it was finished” at the death of Jesus, but incorporated the resurrection of Jesus (cf. Rom 4:24-25); he also tries it in against the Roman Mass where Christ’s sacrifice is re-presented on an iterative basis. While I don’t agree completely with the following (Calvin held to a forensic view on the nature of the atonement), his comments does show that many “pop Protestant apologists” are guilty of a dangerous heresy by downplaying the bodily resurrection to the saving work of Christ (as well as his high priestly intercession [Rom 8:34; Heb 7:24-25; 1 John 2:1-2, etc]):
He repeats the same word which he had lately employed, Now this word, which Christ employs, well deserves our attention; for it shows that the whole accomplishment of our salvation, and all the parts of it, are contained in his death. We have already stated that his resurrection is not separated from his death, but Christ only intends to keep our faith fixed on himself alone, and not to allow it to turn aside in any direction whatever. The meaning, therefore, is, that every thing which contributes to the salvation of men is to be found in Christ, and ought not to be sought anywhere else; or—which amounts to the same thing—that the perfection of salvation is contained in him.
There is also an implied contrast; for Christ contrasts his death with the ancient sacrifices and with all the figures; as if he had said," Of all that was practiced under the Law, there was nothing that had any power in itself to make atonement for sins, to appease the wrath of God, and to obtain justification; but now the true salvation is exhibited and manifested to the world." On this doctrine depends the abolition of all the ceremonies of the Law; for it would be absurd to follow shadows, since we have the body in Christ.
If we give our assent to this word which Christ pronounced, we ought to be satisfied with his death alone for salvation, and we are not at liberty to apply for assistance in any other quarter; for he who was sent by the Heavenly Father to obtain for us a full acquittal, and to accomplish our redemption, knew well what belonged to his office, and did not fail in what he knew to be demanded of him. It was chiefly for the purpose of giving peace and tranquillity to our consciences that he pronounced this word, It is finished. Let us stop here, therefore, if we do not choose to be deprived of the salvation which he has procured for us.
But the whole religion of Popery tends to lead men to contrive for themselves innumerable methods of seeking salvation; and hence we infer, that it is full to overflowing with abominable sacrileges. More especially, this word of Christ condemns the abomination of the Mass. All the sacrifices of the Law must have ceased, for the salvation of men has been completed by the one sacrifice of the death of Christ. What right, then, have the Papists, or what plausible excuse can they assign for saying, that they are authorised to prepare a new sacrifice, to reconcile God to men? They reply that it is not a new sacrifice, but the very sacrifice which Christ offered. But this is easily refuted; for, in the first place, they have no command to offer it; and, secondly, Christ, having once accomplished, by a single oblation, all that was necessary to be done, declares, from the cross, that all is finished. They are worse than forgers, therefore, for they wickedly corrupt and falsify the testament sealed by the precious blood of the Son of God.
