What do Christians mean when they say that people need to be "saved"?
Do we mean that people need to just modify their behavior and obey God's law? It would be great if it were that simple, but that is not what we mean.
It means, rather, that human beings are prisoners, captives and slaves to their idols, to their own lusts, to the world system and to the devil. That we cannot extract ourselves from these things because, like those who have Stockholm syndrome, we have fallen in love with our captors, i.e. we love those things which are doing us the most harm. And while we all vaguely recognize that something is not right in the world and with the nature of human beings, we tend to shrug this off, suppress and ignore it, and willingly come under the illusion that we live in freedom. We cling to the falsehood of human progress and and think human ingenuity will somehow deliver us from ourselves and our problems.
We pridefully hold to the false idea that we are something and can do something to make things right. But in the end we cannot extract ourselves from our captivity. No wisdom, no plan, no power, no understanding, and no technology can do so. The problem runs far too deep in us for that. Like the Hebrews in Egypt we are slaves needing rescue from our captivity. The tyranny of our idols and lusts are too powerful for nature to conquer. We need redemption from the outside.
So salvation is not behavior modification. No. We are too entangled in the web of our own making to get out. We first need supernatural intervention by One like us who breaks the bonds and leads us out of slavery. Then, and only then, after being freed from our captors are we free to do right, to love mercy and do justly and to walk humbly with our God.