I think the old adage of "walk a mile in my (his/her) shoes" is a useful one. In the entire gamut of emotional responses, often multiple responses are all appropriate: frustration, anger, sorrow, compassion, disdain.

I don't know if God says to love everyone. But I do think God says "I love everyone". For me, its less about doing what God says, and more about trying to grasp God's heart, so that I can emulate that. Because his heart is best.

But where does that love come from? What is God's viewpoint, such that he can love everyone, and feel sorrow at any suffering, great or small, warranted or not?

It's the disconnect from God's heart that leaves us unable to grow our own heart, so learning about God's viewpoint (aka learning to see from God's viewpoint) and then experiencing God's heart is key to growing our own. And that's essentially why humans are created: to grow our heart, so that our capacity to give and receive the love (which underlies all things) is matured and perfected. The perfection of our heart comes when God's heart is my own heart, when God's sorrow is my sorrow, when God's joy is my joy.

To understand God we need to learn, step by step, to put ourselves in God's position (I mean, in terms of heart). To walk a mile in God's shoes.

If you have had children, this is invaluable. You love your children, even if you feel anger, hurt, sorrow, disappointment. That love is unconditional; it doesn't stop just because they do.

Also, when your child makes mistakes, the love in your parent's heart causes you to reflect: if I had been a better parent, would this have happened? What are my own shortcomings? Is my love for my children enough, or have the limitations in my heart and character impacted on them as they have grown?

From that viewpoint, God feels compassion and a sense of responsibility to even his most wayward of children, even while their behavior angers him, frustrates him, saddens him. All these things stem from love.