In 1Samuel, King Saul lost his throne because he failed to destroy all the Amaliktes. Shortly afterward David was anointed king, however, it is not until 2 Samuel 5 (many years later) that David actually took the throne. During his time of waiting all kinds of terrible things took place: Saul tried to kill David, Johnathan and David formed an alliance to protect David from Saul, Abner, Saul's "General" fought against David after Saul's death, David's own son Absolom campaigned against his Father....there were wars and killings and basically a civil war among the Israelites. Then when the wars were over David took the throne.
Now why did God allow all of that mayhem instead of just crowning David and have it finished? Why the wait for David?
Those questions can only be answered by God. God does things in his own time and our job is to trust Him even if we do not know why things happen the way they do. God's will, will be done. Our job is to trust him no matter what. TIME is nothing to God. It is everything to us. No matter how slowly time goes by, and no matter what happens, God is to be trusted. Our job is to trust, not to reason why. The only thing that matters is what God wills and what God thinks.