Sardinas is one of the Rangers' top prospects, coming in fourth on the Rangers' Baseball Prospectus top-10 list. He is a plus defender at the shortstop position and a plus-plus runner, both of which are skills that are ready to translate to the major leagues right now. Of course, in Texas, he won't be playing much shortstop. He does have 15 games at second base to his minor league credit. As a hitter, Sardinas still has a way to go and is not major league ready. At just 20-years-old, Sardinas has just 42 games in Double-A on his resume and has yet to have success with the bat at the level. As a switch-hitter, he does offer the Rangers some flexability, and despite not having played anywhere them before, his skill set does project that he could handle third base and the outfield, if the Rangers needed.
For an explanation of this move, one must look no further than the Rangers 40-man roster, where Scott Lucas of The Newberg Report points out that Sardinas is the only remaining healthy position player. With OF Jim Adduci heading to the DL, the Rangers had the choice of either calling Sardinas up early or designating someone for assignment, something they were not prepared to do. Instead, Sardinas has joined the team in the majors, but it's unlikely that he'll see much playing time, other than as a pinch runner or defensive replacement.
The Rangers have not made a statement about how long Sardinas will be in the majors, but one can assume that it is not a long-term plan. Sardinas still needs time in the minors to develop his bat, and to rush him to the majors for an extended period of time could keep that from ever happening. Still, given their 40-man roster situation, the move is understandable, as long as it's not permanent.