Both players have been included in the Spain squad for the World Cup qualifiers against Armenia and Bosnia-Herzegovina after recovering from long-term injuries.
Del Bosque said: "We are already qualified for the World Cup and we only have five games before the tournament - two now, two more in November and one in March.
"We have to profit from them to the max.
"This is the group that will represent us in South Africa.
"That doesn't mean that this is a closed list, but we cannot be whimsical or go ahead shaking it up all the time."
Del Bosque also revealed the reason behind the inclusion of a greater number of players.
He added: "We called up 24 because we have two games, because there is intense club competition, and for the very purity of the tournament - because Bosnia and Turkey are playing to qualify."
Strikers: Guiza (Fenerbahce), Mata (Valencia), Silva (Valencia), Torres (Liverpool), Villa (Valencia).