God loves all humans, but does his love have limits? Can God love a person like Adolf Hitler, who killed millions of people who believed in him? What about serial murderers? Could God forgive a person like Hitler, if he was to come to faith?
ericgorr's answer is really good, but let me write a slightly simpler one.
Yes, absolutely God does love everyone. He totally wants the best for them and wants them to be the perfect person they were intended to be.
Now the trouble is that for Hitler, being the best he was intended to be absolutely involves not killing millions of people and starting a huge war. So God really really wants him to stop doing that - and not just because millions of people are dying, but also because doing this is screwing up Hitler as well and turning him into something he wasn't meant to be. Because of this God hates all the things that Hitler is doing, but still loves Hitler himself. Christians say that God "hates the sin but loves the sinner".
So let's imagine that in 1945 Hitler, instead of killing himself in a bunker, realises that he has been doing entirely the wrong thing this whole time, and is really sorry and genuinely wishes he had never done all those bad things, and asks God for forgiveness. Christians call that repentence. It's as vital to the process of getting right with God as 'coming to faith' is. Because God loves him, and because of Christ's death, God would forgive Hitler. That's pretty fundamental to Christianity.
Forgiveness doesn't mean there are no consequences. Had Hitler repented and lived he would probably still have been tried for war crimes, would certainly have been punished and hated by many people, would probably have been executed. Some Christians believe he might have spent a long time after death in a place called purgatory before going to heaven, possibly to get over the horror of understanding what he had done. Repentance is not an 'easy way out' like a get-out-of-jail-free card. And doing bad things and planning to repent afterwards doesn't work, because that means you thought the things you were doing weren't really bad after all.
There you go. I hope that's a helpful alternative to the more complete answer.
God loves all humans, but does his love have limits?
Could God forgive a person like Hitler, if he was to come to faith?
From the LCMS FAQ on forgiveness & repentance:
Q: I don't really understand repentance. Is it being sorry for your sins and confessing them to God or does it mean to stop committing a certain sin? Like if you are stealing, does repentance mean to stop stealing, because that would mean we can stop sinning and we know we can never stop sinning. I have sins that I commit over and over again, not like I did before I was saved, but I still commit them. So if I don't stop committing those sins (repentance), does that mean that I am going to hell? And also, when the Bible talks about how worldly sorrow brings death but godly sorrow brings repentance and life, how do I know which one I have?
A: Repentance means first of all, to acknowledge our sins, to be truly sorry for them. This "godly sorrow" comes from the Holy Spirit convicting us with God's law.
But the Bible also uses the work of repentance in a broader sense to include faith in Jesus our Savior. This faith is produced by the Holy Spirit, who convinces us through the Gospel that our sins are forgiven for the sake of Jesus, who lived, died and rose again for us.
Put those two concepts together and you have repentance in its fullest sense. (Jesus told His disciples in Luke 24:47 that repentance and forgiveness of sins will be preached in His name to all nations.)
According to the Bible, those who are truly sorry for their sins and trust in Jesus as their Savior also want to turn away from their sins, intending with the help of the Holy Spirit not to keep on living a life of sin. If we want to keep on sinning, we need to ask ourselves if we have really repented. However, we are weak human beings and although we do not want to commit the same sins again and again, we may sometimes fall into sin out of weakness.
Whenever we sin, we know (as John says) that "if we confess our sins, [God] is faithful and just and will forgive our sins" for the sake of Jesus our Savior (1 John 1:9). If repentance becomes a "game" with God and we don't really want or intend to stop committing a certain sin (say stealing), and we go on stealing, living always in that sin of stealing, then we place ourselves in grave spiritual danger. We need to ask that God the Holy Spirit to give us the power to stop committing that sin and trust Him to help us fight against it.
Sad to say, the desire to sin may come back at times, for which we will have to repent again. That's not the same as living in sin. We all commit all kinds of sins daily, for which we have to daily repent. As long as we are sorry for our sins and believe that God forgives our sins for Christ's sake, we will be forgiven and have eternal life.
Worldly sorrow is the kind of sorrow Judas Iscariot had, which caused him to commit suicide. It was a self-centered remorse and despair that wrongly concluded that all was lost in this life, that there was no hope, that there was nothing God could do. Second Cor. 7:10 says that this kind of sorrow brings death. But godly sorrow is true sorrow over sin accompanied by trust in Jesus for forgiveness. This is the kind of sorrow Peter had after he denied Jesus, and King David had after he committed adultery and murder (Psalm 51). Godly sorrow leads to life and salvation, because it includes faith in Jesus Christ.