Substitutionary atonement

Substitutionary atonement is a doctrine in Christian theology which states that Jesus of Nazareth died – intentionally and willingly – on the cross as a propitiation, or substitute, for sinners. This doctrine presents Jesus' death as a supreme act of love for mankind, in order to bring people into a relationship with God. It stresses the vicarious nature of the crucifixion as being "instead of us". This vicarious and substitutionary nature of the atonement is expressed in Scripture verses such as "He himself bore our sins in his body on the tree, that we might die to sin and live to righteousness," (1 Pet. 2:24) and "For Christ also died for sins once for all, the righteous for the unrighteous, that he might bring us to God," (1 Peter 3:18).

http://en.wikipedia.org/wiki/Substitutionary_atonement