"When my time comes, I should be sorry if the only plea I had to offer was that of justice. Because it might mean that only justice would be meted out to me."
("The Murder At The Vicarage", Agatha Christie)
The objective here is not to discourage justice or undermine it's importance in society. After all, it's when people are satisfied that the law is made for their own benefit and a failure to obey it is duly penalized without discrimination, rights are given after responsibilities are fulfilled, and good is fairly rewarded and evil justly punished, ...only then are they more inclined to behave in a decent and civilized manner, and thus peace is maintained.
What this quotation actually does, is to compel us to acknowledge that on the Day of Judgement, when we will stand before God, it's not justice that we would desire, rather it's mercy for which we will plead.
If at that time, the best that we could say of ourselves is that we had always been fair and just in our dealings with others, then it might be that only justice would be meted out to us.
However, if on the Day of Judgement, we could honestly claim that we had usually implemented tolerance, compassion and forgiveness towards others throughout our lifetime, ...then hopefully we would have more chance of achieving mercy from God. (Amin).