He died for us” means he died on our behalf.  He died instead of us. It also means he died to represent us. So whatever happened to him applies to us. Paul says, “We are convinced that one died for all and therefore all died.” (2 Cor 5.14).  His death was our death (a more complicated explanation of this can be found in Rom 5.12-21).

The benefits of Christ’s death apply to everyone who belongs to Christ. That is, those who believe in him. Paul says that when we were baptised into Christ, we were baptised into his death (Rom 6.3). This means that “we will certainly also be united with him in his resurrection.” (Rom 6.5). He was raised from the dead so that we can live a new life.

There is more to the answer of course. He died for us because of his great love and mercy. He died for us because we have no other way of gaining God’s forgiveness. He died for us in order to bring us to God.

And who is “us”? Only those who trust in the Lord Jesus Christ and believe his death was for them.  John put it neatly:

For God so loved the world that he gave his one and only Son, that whoever believes in him shall not perish but have eternal life. (John 3.16).

Dale