Question 62: But why cannot our good works be the whole, or part of our righteousness before God?

Answer: Because, that the righteousness, which can be approved of before the tribunal of God, must be absolutely perfect, (a) and in all respects conformable to the divine law; and also, that our best works in this life are all imperfect and defiled with sin. (b)

(a) Gal.3:10 For as many as are of the works of the law are under the curse: for it is written, Cursed is every one that continueth not in all things which are written in the book of the law to do them. Deut.27:26 Cursed be he that confirmeth not all the words of this law to do them. And all the people shall say, Amen.
(b) Isa.64:6 But we are all as an unclean thing, and all our righteousnesses are as filthy rags; and we all do fade as a leaf; and our iniquities, like the wind, have taken us away