There is one regular episode left before the finale …
In season six we see Jacob appear to Hurley when he’s alone, and after Jacob has been killed. This is not Jacob, but the smoke monster posing as Jacob. The smoke monster wants Hurley to show Jack the lighthouse, in which Jacob has watched the candidates for a very long time (e.g. we see the house Jack grew up in). He also wants them to know that Jacob brought them to the island. This information upsets Jack and Jack smashes the mirror at the lighthouse, which is what the smoke monster wanted him to do to prevent people from finding the island.
Hurley then asks “Jacob” why he wanted Jack to go to the lighthouse if Jack was just going to break the mirror. Hurley thought “Jacob” wanted people to find the island. “Jacob” says it is ok because the person coming would find the island another way (this is Whidmore). Whidmore is a rival of the smoke monster because Whidmore created the sonic fence that protects people from the smoke monster.
In season six we also see a teenage boy in the jungle who confronts “Locke”, who always looks quite alarmed when he sees the boy (other people see the boy, too — Sawyer and Desmond). This boy is Jacob.
Now about the numbers. Each candidate was given a number. Jack’s number is 23 and Jack’s last name is Shepherd. Jack is Jacob’s replacement. After Sun, Jin, and Said die on the sub, we are left with Hurley (8), Sawyer (15), and Jack (23). Hurley and Sawyer’s numbers add up to Jack’s number. No coincidence. They will be helping Jack against “Locke”.