WHY NOT 5 ABILITIES?!?

This game is easily one of my favorite mobile games to play. One of the important parts of the game is to level up your characters and you get skill points for every level you gain. You use the skill points to gain new abilities and things. For my cleric I got the skeleton fighter ability but then I saw I couldnt get the resurrection ability anymore. Why is that? Also for my fighter I either have to choose between the shield or 50% more damage for 10 seconds. I dont understand why I cant get both. I thought you would be able to collect all of the abilities. Whats the point of having skill points if you cant get all of the skills?

Arirenwal about Heroes vs Monsters