Most Americans believe that what their problem is, is something that has happened to them; and their solution is going to be found within. In other words they believe that they have an alien problem that is to be resolved with an inner solution; when the Gospel says that what we have is an inner problem and the only solution is an alien righteousness. (Albert Mohler)
By an alien righteousness, the author means a righteousness which is outside of ourselves, and not one that comes from within us. It’s a righteousness which comes from Christ’s life and not from our own. Our very own righteousness can never be good enough. But thank God for Christ’s righteousness which is now ours by faith.