Hi Lik3, thanks for posting this. It would be best that with that phrase, we will look into the bible. It is indeed true that once saved, always saved. John 3:16 is a good summary of it already. There is this greatest invitation to all "whoever" believes, regardless if they did good or not, shall have eternal life. Life here means zoe life. There are 2 greek uses of life: Bio and Zoe. In this verse, it uses Zoe, the same word used in John 10:10 where Jesus said, I have come that they may have life, and have it to the full. That's His promise, no conditions. With regards to willful sinning, we need to categorize points about the word "saved". Saved from what? Salvation can be categorized in 3 phases:
Phase 1 is Saved from the Penalty of sin. Jesus paid it all already when He said, it is finished or tetestai or paid in full before he breath his last breath. Jesus has no debt, yet he paid what must be paid - all of our sins and the wage is death. Hence, His death paid it all. Theologians call this Justification where anyone who believes is justified. No more any tarnish of sin because the debt is paid. Hence, the believer then is called Just.
Phase 2 is Saved from the Power of Sin.This now will answer about your question of willful sinning. Everyday from the moment we wake-up til we go to bed, we are in constant battle. Why, still because of Sin that is inherent in us. From the time that God justified us (that moment that we believe in Jesus and the work He had done on the cross) He never never never had taken His eyes from us. We are the apple of His eyes, and daily moment by moment He saves us. Meaning, His love endures forever. His faithfulness is new every morning. Because of His mercy we are not consumed. Sin is no longer an issue to God. The issue is, would we enjoy the abundant life here on earth as He promised if we disobey? I doubt so. Are we yielded to Him? This is the most difficult phase because it requires our daily submission to the leading of the Holy Spirit. I cannot deny that I willfully disobeyed Him. Does that mean that the death of Jesus on the cross was forfeited. I know that there is struggle deep inside to abide with my willful lust or to abide in the Power of God. I have the freedom to choose. Now, if we obey - expect blessings like joy, peace, love, etc. The opposite, if we disobey, expect chaos. What is amazing with our God is that, out from any chaos, still something good will come out of it in that experience. Of course, we already miss a lot of blessings. Blessings in time and Blessings in eternity. In time - could be productivity, wealth, wisdom, frienships, etc. many.. In eternity - silver, gold, precious stones, crowns - which we will present to our greatest Lover, the Groom, and no else but Christ Jesus and we the believers the bride. The opposite: wood, hay, straw. Fire will test it. This phase in our life is called Sanctification, being set apart daily, purified daily, polished daily, processed daily, that we will come out so precious in His sight. That is, if we obey. If not, well heaven will still have celebration for the fast forwarded life of a saint to eternity.
The unfinished purpose. I wonder how would that be before Christ. The bible is clear, there will be judgement before Christ Jesus. again, sin is not an issue to God but it is to us. I pray that i finish well.
Phase 3, the most awaited time of the Christian. Saved from the Presence of Sin, where the corruptible body will be changed to incorruptible. There is no pressure of sin anymore. No more sorrows or deep frustrations, sickness, anger, bitterness and all of the baggages in life. So free from all of this world's pulling down effect. The day I am waiting for. That blessed hope.
Hence, in Christ, once saved will always be saved, regardless.