We've all hurt those whom God loves, therefore we've all sinned against God (See Romans 3:23).
Yet God is always doing his very best for each of us.
If someone is always doing their very best for you, if they could not do more for your good, you would have to conclude that they are not holding anything against you. You would have to conclude that if you have done something which offended or hurt them, they have forgiven you. Because God is always doing his best for each of us, we must conclude that God has forgiven each and every one of us. God unconditionally accepts all of us.*
"But," some will say, "You must repent to be forgiven. Why does God offer us forgiveness if we are already forgiven?"
There are two types of forgiveness from God. One is unconditional and one is conditional. One is given to everyone, and one is offered to everyone. The first, which I've already mentioned, simply means to love perfectly.
Since we are loved perfectly, and God is always doing his very best for us, he expects us not to hold anything against others and to do our best for them.
After telling the parable of the unmerciful servant in Matthew 18, Jesus said,
“This is how my heavenly Father will treat each of you unless you forgive your brother or sister from your heart.”
The unmerciful servant was forgiven an incredible amount, yet he did not forgive the one who owed him a little, and instead treated him harshly. He should have been merciful; he should have forgiven because of how much he had been forgiven. Not only that, but he forgot how much his master loved his fellow servant (see here).
So in this parable Jesus is telling us that we should forgive others no matter what they've done. He's telling us that we must unconditionally forgive, in the same way God has unconditionally forgiven each of us (See Colossians 3:12, 13 and Matthew 5:43-48).
So what is the conditional kind of forgiveness?
"If your brother or sister sins against you, rebuke them; and if they repent, forgive them" (Luke 17:3).
What's the very best we can do for this brother or sister in this circumstance? It's to warn them and not pretend that nothing has happened. Why? The kindest thing we can do for them is to show them that what they are doing is harmful. The conditional forgiveness is because of the unconditional forgiveness--love. (See also Lev 19:17).
When God doesn't forgive, he doesn't forgive because of love. When he doesn't forgive it's because he's trying to destroy the sin in us which is destroying us. He's trying to destroy our hatred, our lack of kindness, our lack of love.
"For if you forgive other people when they sin against you, your heavenly Father will also forgive you. But if you do not forgive others their sins, your Father will not forgive your sins" (Matt 6:14, 15).
"But won't we worry if we're not sure if we've been forgiven? How can we be free if we are worried about whether or not we have been forgiven?"
You can't be free while you worry about that. So what's that solution?
Focus on the kind of forgiveness God has given you but focus even more on how much he loves those around you (See Love Makes Everything Lovely). Then out of gratitude you will find you are able to love even those who try to hurt you.
"We love because he first loved us" (1 John 4:19).
Only those who don't know God are afraid of his punishment. When you know God you will not be afraid of his punishment; you will welcome it, because you know that if he punishes you it's for your good (See Hebrews 12:6).
Know this, all God does for you he does for your good. He even became a man and died for you just to open your eyes to how much he loves you.
* This seems like a contradiction because God can do more and he want's to give us more. So how can I say God is doing his very best for us?
“Man finds it hard to get what he wants, because he does not want the best; God finds it hard to give, because He would give the best, and man will not take it.” - George MacDonald.
If we ask God, sometimes he will give us things that he would not have given if we did not ask. The purpose of the giving is so that we might come to appreciate the giver. The giver is better than the gift. See Prayer.