Make the scratching post attractive to your cat by rubbing catnip over it. Place a toy that dangles on top - that should get his attention. Or place favorite treats at different levels. You can try scratching it yourself and maybe that will show him what it's for. Cover the areas elsewhere that he uses as a scratching post with 2-sided sticky tape. There are also sprays that available that are safe, but have a smell that cats don't like and will discourage your cat from using the furniture as a scratching post. Keeping his nails trimmed helps too.
