Samuel finds himself rather frustrated in his old age. His sons have turned out to be selfish and corrupt. The nation of Israel has continually refused to be true to God or each other. In spite of God repeatedly delivering them from all sorts of oppression, they eventually want a king to deliver them. As far as Samuel is concerned, Israel has sold out. His own people have abandoned their heritage, and in so doing, stood opposed to him and everything he represented as a judge in Israel.
As Saul learns more and more about what it means to be a king, and as such gains more influence, Samuel finds himself pushed further and further into the margins. He is old. He can no longer lead armies. His family is a disappointment, and where once Israel listened to his advice, now they ignore him. Samuel has one last speech left in him, however, and by the end he has finally brought his audience to a place where they can see how they have turned their backs on God, which is why they demanded a king in the first place.
When Israel comes to this realization, the people ask Samuel to go to God on their behalf. If I were Samuel, I would probably be thinking, "Oh sure, you abandon and reject me. You abandon and reject God, and now you want me to come to the rescue? Forget it." But, that isn't Samuel's response. Samuel's response is this:
"...As for me, far be it from me that I should sin against the LORD by ceasing to pray for you; and I will instruct you in the good and the right way."
Israel and Samuel found themselves on opposite sides. Israel, Samuel's own people had effectively become his enemies, but Samuel's response to them in their time of need wasn't to laugh and say, "To hell in a hand basket with you all." His response was to love his enemies, even though in this case those enemies might have been friends. There's a reason Samuel was the man of God during his day and age.
As the phrase goes, God is the same yesterday, today, and tomorrow. Jesus is the full revelation of God, not a redefining of God. Assuming otherwise is a misunderstanding on our part. As such, God has always expected the same behavior from the people who claim to follow him. Love God. Love your neighbor. Love your enemy.
Stopping point: I Samuel 12