March 2: D&C 4:3

3 Therefore if ye have desires to serve God ye are called to the work;

That means if you think even sligtly that serving God sounds like a good plan for you (and who wouldn't with the promise that he gives in the verse above this one (refer to yesterday...which wasn't really yesterday)) then you are called to serve him. He wants those who want to serve him to serve him. I also think it's important that he specifies that you have to want to serve God. It's a great point, that applies to missionaries nowdays, how effective are the missionaries that don't really want to serve God? I would say not very effective. So really you have to want to serve God, and once you want to serve God, then you need to serve him wholeheartedly to get the blessings promised (again refer back to yesterday).