There are various versions of how this works: the most common being a very primitive and barbaric suggestion that Jesus died in our place. Such a claim presents a view of God that is hardly lovable.
So I don't prefer to think of today as the day of remembering how Jesus "died in our place" or some other such weird notion.
What I choose to remember is that Jesus was crucified by imperial power. The reason, historically, that Jesus was executed - think about that executed! - was because he disturbed the status quo. In the name of the Kingdom of God - the Jewish God of justice and peace - Jesus condemned the ways of empire, and the system of domination and exploitation.
The death of Jesus was a direct result of his passionate commitment to peace, justice, and compassion in the name of God and God's kingdom. That is what ought to be remembered.
The great Medieval theologian Peter Abelard argued that Jesus' death should not be understood as a substitution or a ransom paid, but as an example of divine love. An example that, if we truly contemplate it, transforms us so that we become better people.
Abelard, it seems to me, was right. The importance of the death of Jesus is that it shows how committed he was to the central goal of his life, and inspires us to be just as committed.
The religious importance of this death, for Christians, is this: Jesus' death was not merely the result of his commitment to justice and compassion. Rather, it was also his firm conviction that God is found chiefly in a life of Justice and compassion; a life he himself embodied.
Note: I originally published this post last year. I thought it worth re-posting