Contradiction between God's mercy being greater than ours and Jesus' harsh words about who will end up in hell We believe that God is supremely good and merciful, far more than we are. At the same time, I see in myself that I would not condemn anyone to hell, even villains like Hitler and Stalin. Perhaps I’d have them spend a long time being purged and making up their faults, but at the end I’d let them into eternal happiness, assuming they want to be there, of course. The only case when someone would be “sent” to hell is if he simply wants to be there and is not willing to change his mind, even upon seeing the entire truth about all reality. 

Then, if I feel this way, is it possible to imagine that the good God would be less merciful than this, and not somehow even more? Yet, various passages in the Bible (including Jesus' words in NT) as well as the traditional teaching of the Church suggest just that. That it’s not just total evildoers, people entirely corrupted, ones who would obstinately prefer eternal solitude to eternal connectedness - who go to hell. It seems that it’s also people who slipped up through weakness, who followed their sense of good even when knowing the Church teaches otherwise, or who were not watchful enough. 

How to understand this? How to truly love and trust God in Whom there appears to be such a contradiction?

Note: I'm writing this question from a Catholic perspective.
The Apostle Paul outlined for us a definition of Love. Mercy falls under that larger category. So can we measure the degree of Christ’s love by that standard? If Jesus perfectly exemplifies love by his actions, then we must conclude that the motive behind his admonitions about Hell was one of Love.


  Love is patient, love is kind. It does not envy, it does not boast, it
  is not proud. It does not dishonor others, it is not self-seeking, it
  is not easily angered, it keeps no record of wrongs. Love does not
  delight in evil but rejoices with the truth. It always protects,
  always trusts, always hopes, always perseveres. (1 Corinthians 13:4-7,
  NIV)



Patience. While hanging on the cross, did Jesus call for legions of angels to rescue him and destroy his enemies? No, he prayed for forgiveness. How long has Christ’s patience persisted? 2,000 years! Yet he says that he will return and execute judgement at that time. Why the delay? Saint Peter told us:



  But do not forget this one thing, dear friends: With the Lord a day is
  like a thousand years, and a thousand years are like a day. The Lord
  is not slow in keeping his promise, as some understand slowness.
  Instead he is patient with you, not wanting anyone to perish, but
  everyone to come to repentance. (2 Peter 3:8-9, NIV)



Kindness. A pastor once told me that kindness is seeing someone else in need and acting to meet that need. What did we need? A savior to take our place, pay for our sins, and rescue us from Hell. We did not need someone telling us lies, like God is not just and will overlook all our sins without anything being done about it. Jesus did the most that anybody can do for another person: he gave his life. No greater sacrifice can be made. No greater mercy can be shown.
Envy, boasting, pride. Jesus refused the devil’s tempting appeals to pride: you deserve an easy life, well protected, in command of the kingdoms of the world. He was silent before his accusers. As Paul said in Philippians:



  Who, being in very nature God, did not consider equality with God
  something to be used to his own advantage; rather, he made himself
  nothing by taking the very nature of a servant, being made in human
  likeness. And being found in appearance as a man, he humbled himself
  by becoming obedient to death— even death on a cross! (Philippians
  2:6-8, NIV)


Who ever gave up so much privilege to serve others as Jesus? That is humility.


Honoring others. Whom did Jesus honor? A tax collector. Women of ill-repute. Peter, who denied him, yet was appointed head of the church, and Paul, a persecutor Of Christians. 
Unselfish. Christ was not self-seeking. First, he sought to accomplish his father’s will. Second, he said:



  Greater love has no one than this: to lay down one’s life for one’s
  friends. (John 15:13, NIV)


Jesus told us how to measure Love. He lay down his life for his friends, thinking not of what it would cost him (selfishness), but what it could accomplish for those he loved (selflessness). He demonstrated ultimate love in two ways: he gave all his life away, and that life, being the life of God, is the most valuable life in the universe.


Protects. I skip ahead to get to the point of the discussion. Jesus protects. What do we ask for in the Lord’s Prayer? Deliver us from evil. The church is always at prayer, saying “protect us, Lord, from every evil, and grant us peace in our day...” Those who trust in Jesus are protected from the destructive evil within our souls by the sanctification purchased for us. We are also protected from the evil of all who reject that sanctification, hence remain a source of deadly peril. God’s mercy to us is to protect us from all who cling to evil. Imprisoning the unrepentant in Hell enhances God’s mercy, it does not take away from it.


The final question is always: but maybe if people were given just a little more time?


  “If the Lord had not cut short those days, no one would survive. But
  for the sake of the elect, whom he has chosen, he has shortened them.
  (Mark 13:20, NIV)


If the wicked are given too much time, then the suffering they cause will become so severe for God’s children that some of them will fall.  In engineering, we call this the point of diminishing returns. God will not let that happen.

On a personal note, when I was younger, a Christian urged me to stop rebelling against a God and warned me about the consequences: I would go to Hell. I needed that warning, and I heeded that warning. Those harsh words saved my soul and set my life on a new path. Which would be more merciful, to be polite and leave me to die in my sins? Or “rejoice with the truth”?