I did not know Calvin professed to be completely loyal to the teaching of St. Augustine as a quote of his showed earlier. Regardless, Calvin imho disagree with St. Augustine on several important points. For e.g. St. Augustine taught the justified can fall from the Faith.
Chapter I: "I Have now to consider the subject of perseverance with greater care; for in the former book also I said some things on this subject when I was discussing the beginning of
faith. I assert, therefore, that the perseverance by which we persevere in Christ even to the end is the gift of
God; and I call that the end by which is finished that life wherein alone there is peril of falling. Therefore it is uncertain whether any one has received this gift so long as he is still alive. For if he fall before he dies, he is, of course, said not to have persevered; and most
truly is it said. How, then, should he be said to have received or to have had perseverance who has not persevered? For if any one have continence, and fall away from that
virtue and become incontinent — or, in like manner, if he have righteousness, if patience, if even
faith, and fall away, he is rightly said to have had these
virtues and to have them no longer; for he was continent, or he was righteous, or he was patient, or he was believing, as long as he was so; but when he ceased to be so, he no longer is what he was. But how should he who has not persevered have ever been persevering, since it is only by persevering that any one shows himself persevering — and this he has not done? But lest any one should object to this, and say, If from the time at which any one became a believer he has lived — for the sake of argument — ten years, and in the midst of them has fallen from the
faith, has he not persevered for five years? I am not contending about words. If it be thought that this also should be called perseverance, as it were for so long as it lasts, assuredly he is not to be said to have had in any degree that perseverance of which we are now discoursing, by which one perseveres in Christ even to the end. And the believer of one year, or of a period as much shorter as may be conceived of, if he has lived faithfully until he died, has rather had this perseverance than the believer of many years' standing, if a little time before his death he has fallen away from the steadfastness of his
faith."
https://www.newadvent.org/fathers/15121.htm
St. Augustine taught Justification/Sanctification PLUS Perseverance = Full Salvation. That means, if you persevere, you are saved. And if you are granted perseverance (which St. Augustine said no one can know for certain), the only way you prove it is by persevering.
Free Grace said:
Also, anyone who believes they have a verse that does indicate that salvation can be lost are basically saying that the Bible is internally contradicted.
Strictly speaking, it is not "salvation" that can be lost. It is Justification/Sanctification that can be lost.
Can you explain Hebrews 10:29? It speaks of those truly Sanctified by the Blood of Christ who fell away.
They did not lose Salvation (Justification+Perseverance), they lost Sanctification alone, which they once had.
Regarding John 10, there the Lord is speaking of those He gives the Gift of Perseverance. These will never perish.
Recall that the Lord had said:
"Many are called, but few are chosen". Many are called to Justification, but few are chosen for Perseverance. I think Calvin may have wanted to follow Augustine, but unfortunately he confused Justification and Perseverance.
God Bless.