When we sin, we offend God. By offend we mean we have acted contrary to the will of God. It dosen’t mean that we have hurt or cause him any pain since he is perfectly happy always and nothing could interrupt that love and happiness ever.
Then how is it that we say that when we sin we hurt God, especially his sacred heart? For it seems to be a rather familiar thought that the sacred heart of Jesus is in some way hurt when we sin. We can see this especially in the private apparitions of Jesus and what he said in them. That his sacred heart burns with desire to forgive sinners if they would but just turn to his merciful heart and ask for forgiveness. And that it pains him to see anyone who would turn away from him.
What this means is that he loves and died for every individual who ever lived, and suffered greatly in order to reasure them of his devotion and love for them … that he gave his all so that everyone could be with him someday in his home happy with him forever. In that sense, it does “hurt” because he wants noone to go without ever being happy and so he “feels” this loss for those who have turned away … not for his own happiness, but because he loves them very much and “feels” their terrible loss.
He also “feels” for those who do not accept his mother, which is also their loss.
So at Fatima …
After Lucia had been praying, Our Lord revealed the reason of the 5 Saturdays of reparation: "My daughter, the reason is simple: there are 5 types of offenses and blasphemies launched against the Immaculate Heart of Mary:
1 Blasphemies against its Immaculate Conception.
3 Against its Divine Maternity, at the same time refusing to receive it like Mother of mankind.
4 Against those that publicly try to instill in the hearts of children, the indifference, the scorn and even hatred towards the Immaculate Mother.
5 Against those that scorn Her in her sacred images."
Our Mass is also a reparation, that of the sacrificial lamb offered on our altar, that was first offered on the altar of the cross. So also by our own prayers, sufferings, works, we too join with the sacrificial lamb to offer reparation. And one of the reparations that is performed is to offer reparation for the denial and hostility shown toward Jesus’ thru the disrespect shown to his mother.
And one way to do this is to join Mary in the sorrows she experienced because she loved her son so very much. The sorrows in her heart are but the reflection of her love and so when we join her in her sorrows, we too are expressing this strong love for Jesus.
What we do does make up for what others fail to do or the disrespect shown to Mary and Jesus. And when we do this, we not only increase our own love for Jesus and Mary, but also the graces that this love brings to us.
But not all will understand this because this depends on love. Commandments, precepts, laws, rules, do not always have their basis in love. Not all are interested in making it up to Jesus for the offenses of others, but are concerned with how much they can do and still squeak by. So it may not make much spiritual sense to these.
But if someone has a true love for Jesus, then it isn’t just a matter of their own sins they are sorry for, but also for the sins of others. And their desire is to make up for those other sins out of love for both Jesus and their neighbor.