"Even Roman Catholics believe that salvation is by grace... that is not the issue...and never has been ... the issue is that salvation is by grace ALONE. In other words, Jesus is not only necessary but sufficient to save us to the uttermost."
Sadly, even many Protestants claim they believe in "grace alone" in their confession but deny it with their theology. In many cases, such claims are largely meaningless and without substance. For example, if you believe a man can lose his salvation then, by definition, you already affirm that YOU must maintain your own just standing before God. Christ may be necessary in the process but He only partly helps - or maybe even contributes a large part. But "part" is not "all" of Christ, or else loss of salvation would be an impossible supposition ... but because there is something you could do to lose it, you must, therefore, maintain it. With the help of grace yes... but such grace, by itself, is not enough if you can do something to lose it ... it is grace plus my effort. That is not "All of Christ" or "Christ alone" by any definition.
Christ secures salvation for us, rather, because He provides EVERYTHING we need for salvation.(Hebrews 7:23-25) He does it all, without mixture with any merit from without. This is the normal meaning of "alone". One has to do major verbal gymnastics to attempt to claim "oh yes, we must do something to maintain our right standing before God" and yet still claim that we are saved by "Christ alone". It is a meaningless statement. The reality is, by the grace and mercy of Christ, we do work and we do persevere, not in order to maintain God's favor, but because we already have it as he has made us His children. If grace were conditional and God had conditions for us to keep our standing as his children, it would be an oxymoron. Grace would no longer be grace. It is grace because he already knew the worst about us and yet made us his children, in spite of what He knew.
“Behold, I have come to do your will... And by that will we have been sanctified through the offering of the body of Jesus Christ once for all...For by a single offering he has perfected for all time those who are being sanctified." (Heb 10:9-10, 14)