"His lord said unto him, Well done, thou good and faithful servant: thou hast been faithful over a few things, I will make thee ruler over many things: enter thou into the joy of thy lord."

                             -Matthew 25:21

Jesus taught us through this parable (25:14-30) that we must first prove our faithfulness in little things before God will trust us with bigger things. Many times we want the Lord to use us in a big way, yet we are unwilling to fulfill our smaller obligations, claiming that those things are "insignificant", or "don't really matter." We want God to send us halfway across the world as a missionary, but we ignore Him when He tells us to talk to our neighbor across the street about the Gospel. We want to be used to negotiate peace with foreign nations, yet we can't even get along with the members of our own household.

"He chose David also his servant, and took him from the sheepfolds:
From following the ewes great with young he brought him to feed Jacob his people, and Israel his inheritance.
So he fed them according to the integrity of his heart; and guided them by the skilfulness of his hands."

                            -Psalm 78:70-72

When God was looking for somebody to make king over Israel, He looked for someone who was already proving their faithfulness to Him. David had to first show that he could lead a flock of sheep before the Lord would entrust Him with the leadership of an entire nation. We have no record of David complaining that being a shepherd was a waste of time or insignificant. Instead, he used that time to practice the skills he would need later in life (leadership, bravery, patience...), as well as to draw closer to God. Obviously, that time was by no means wasted because He ended up being the greatest king Israel would ever have.