From Stephen Charnock's Existence and Attributes of God [Goodness]:

It is the disease of human nature, since its corruption, to hope for eternal life by the tenor of the covenant of works. Though this ruler’s conscience was not thoroughly satisfied with what he had done, but imagined he might for all that fall short of eternal life, yet he still hugs the imagination of obtaining it by doing (ver. 17); ‘What shall I do that I may inherit eternal life?’ This is natural to corrupted man.