Abel gave a more acceptable offering than Cain because the animal to be sacrificed in faith represented a substitutionary sacrifice, symbolic of the perfect sacrifice of Christ, the only payment through which our debt can be paid in full. It is useless for the sinner to bring anything of his own to pay the debt; we are obligated to trust in faith as Abel had demonstrated. Abel's faith was a living faith that resulted in obedience; in Cain's there was not.