Why saving grace must be irresistible

The fourth point of Calvinism is Irresistible Grace.  This doctrine says that when God calls us to faith in Jesus he calls effectively; he always succeeds in his purpose to save us.

The Bible distinguished between the general call of God to all sinners to come to Jesus (e.g. Jesus saying “Come to me, all you who are weary and burdened, and I will give you rest”) and the specific call or summons God gives to his elect (e.g. Romans 1:6…you also are among those who are called to belong to Jesus Christ…)
 
John Piper writes: “Irresistible grace refers to the sovereign work of God to overcome the rebellion of our heart and bring us to faith in Christ so that we can be saved”. If the doctrine of total depravity is true, there can be no salvation without irresistible grace. If we are dead in our sins (Ephesians 2:1), totally unable to submit to God, then we will never believe in Christ unless God overcomes our rebellion.  Dead people cannot make themselves alive.  The incredible news of the gospel is not that God makes bad people good, but that he makes dead people alive (Ephesians 2:1-10). 
 
God the Father elects us before the creation of the world. God the Son dies to accomplish our salvation and God the Holy Spirit calls us to himself; we simply respond in repentance and faith, and enjoy all benefits of that salvation. 
Jesus said in John 6:44,  “No one can come to me unless the Father who sent me draws him. And I will raise him up on the last day.”