All Christians are familiar with the fact that when Jesus died on the cross, the sins of the whole world were placed on Him; that was why He died. He died on the cross for us. But another death also took place on the cross. That was when we were crucified with Him (Ga.2:20). This happened in God's mind when He placed us in Christ when He died on the cross, even though we didn't physically exist at that time. We didn't die for our sins; Christ died for that. What was this death that we died with Him? It was our death to sin. God says that Jesus not only died for us -- our sins (1Co.15:3), but He also died to sin (Ro.6:10).
When Jesus died for our sins, He paid the penalty for our sins so that we could be forgiven. But when He died to sin, that was to give us an attitude of hatred towards sin, just as He has, so that we would no longer like to sin but we would hate to sin. This is what we experience when we are born again through faith in Him (Ro.6:1,2). Our response when this happens is that we place our flesh on the cross from our side, because it was through the desires in the flesh that we were being tempted to sin (Ga.5:24).
God tells us to consider ourselves now as 'dead to sin' (Ro.6:11) because that is the new attitude He has given to us. Now we are not to yield any part of our body to commit sin (vv.12,13), because God's grace has taken away our old willingness to sin and given us a hatred for sin instead (v.14).
Now we see that whenever we are tempted to sin, we need to put that desire to death on the cross by the strength the Holy Spirit gives us (Ro.8:13). That is the meaning of taking up our cross daily, denying ourselves and following Jesus (Lk.9:23). In this way we work out our salvation daily, because God is working in us to hate sin and want to do His will, and also giving us help to do it (Php.2:12,13).
We know that our salvation has three phases -- justification, sanctification and glorification. Jesus died on the cross for our forgiveness from which we get justified before God (Ro.5:1) and accepted as His children. He has then started us off on the way of sanctification by giving us a heart that hates sins and wants to do the will of God. When we recognise this, we respond by seeking to keep the flesh crucified and placing each lust on the cross to die as we are tempted daily. This is the process through which our life is being transformed from our old sinful nature to the nature of Jesus Christ. We can see that without the above response from our side, God is unable to provide us this sanctification.
Many Christians who think that God will do everything from His side do not realise that He expects us to respond rightly to the work He does in our heart and mind. Through this process, He wants to reverse the act of Adam and Eve by which they chose to do their own will and deny the will of God. Our salvation will become complete only when we choose to deny ourselves in order to do His will.