Ellen White writes a short paragraph in Steps to Christ which is, in my estimation, one of the clearest and most encouraging explanations of righteousness by faith outside Holy Writ. Here it is:
"Christ has made a way of escape for us. He lived on earth amid trials and temptations such as we have to meet. He lived a sinless life. He died for us, and now He offers to take our sins and give us His righteousness, If you give yourself to Him, and accept Him as your Saviour, then sinful as your life may have been, for His sake you are accounted righteous. Christ’s character stands in place of your character, and you are accepted before God, just as if you had not sinned."
The entire piece is worth memorizing, but especially the last two sentences.