To appoint a King from the Jewish people - "you shall set a King over you..." We need to understand why the prophet Samuel was so angry with the Jewish people when they demanded a king (Sam. I 8:6)...since this is one of the commandments as the Sages taught that 3 commandments were given to the Jews to be fulfilled only once they entered the land...
There are commandments that are to be performed everywhere. There are commandments such as tithes and other commandments that are linked to the land itself and then there are commandments that are connected with the independence and supremacy of the Jewish people in the land -appointing a king, to wipe out the Amalek nation, and to build a Holy Temple. It took roughly 400 years following the entry into the land, until the Jewish people appointed a king. This was at the end of the period of Judges with the appointment of King Saul, about 300 years after the entry into the land. Prior to that there was an attempt at kingship (by Avimelech (Judges Ch.9)) but it was only a small kingship that ruled over several tribes.
King Saul then attends to the task of wiping out Amalek. According to the simple understanding of the text, he might have wiped out an Amalekite base, but he left some Amalekites behind. The rabbis teach (in the Midrash) that King Saul spared the Amalekite King, Agag for one night, and as a result he impregnated a maidservant and continued his lineage, eventually leading to the birth of Haman, the arch-enemy of the Jewish people in the days of the Persian exile. Similarly, the Temple was only constructed by Solomon about a century later. The Tabernacle in Shiloh was an intermediary stage. The took the traveling Tabernacle and planted it in Shilo in a semi-permanent fashion.
A review of Jewish history shows us that the commandment of anointing a Jewish King, wiping out Amalek, and building a Holy Temple are different from other commandments. While most of the other commandments given at Mt.Sinai began being observed right away, these three commandments were "ignored" for centuries. This seems to indicate that a certain "maturity" on the part of the people was necessary before they could begin observing them.
(The text in italics are the words of Derech Mitzvosecha by the third Lubavitcher Rebbe, the Tzemach Tzedek. The bolded words are Rabbi Adin Steinsaltz's commentary as heard on his shiurim on hashefa.co.il. The rest is my commentary. All rights reserved to Rabbi Steinsaltz. Pictures courtesy of Moshe Schlass.)
