A gradual growth in holiness?
A distinct and separate work of grace after salvation?
Something only God can have?
The ability to live a sinless life?
I’m not really sure exactly what sanctification is, but I do know that it is not the ability to live a sinless life. The bible says that the “Righteous man falls seven times and the Lord sustains him.” That would imply that it’s impossible to lead a sinless life. I’m going to have to study this topic for a more solid answer.