Thank you for that excellent question. I believe He spoke those words “I HAVE overcome the world” in ANTICIPATION of the cross. In the very next chapter Jesus prayed to the Father, “I HAVE glorified You on the earth. I HAVE finished the work which You have given Me to do” (John 17:4). Jesus knew that in a matter of hours He would glorify His Father by going to the cross where He would finish the work of atoning for sin so sinners could be saved. You are right that it was on the cross when He actually “finished the work the Father gave Him to do” which enabled Him to cry out “It is finished.” But in our Lord’s words in John 17:4 He was so certain that He would accomplish the work, He spoke as if He had already accomplished the work of atonement. As one has said, “Although the crucial part of that work still lay ahead, the Lord put it all in the past tense. There would be no wavering, no turning back, no failure. He was wholly committed to the work of the cross, as He and His Father both knew. The agony in the garden would not shake this resolve. The indignities and injustices of Gabbatha, the horror of Golgotha, and the silence of the grave were stepping stones on the predetermined way. That the Lord would carry the divine purpose out to fulfillment was never in question. His obedience would stand the test. It was as good as done” (John Phillips).

We should ask another question: How exactly did Christ’s death on the cross overcome the world? Let’s read John 12:23-24, 27, 31-33 where Jesus said, “The hour has come that the Son of Man should be glorified. Most assuredly, I say to you, unless a grain of wheat falls into the ground and dies, it remains alone; but if it dies, it produces much grain…Now My soul is troubled, and what shall I say? ‘Father, save Me from this hour? But for this purpose I came to this hour…Now is the JUDGMENT OF THIS WORLD; now THE RULER OF THIS WORLD WILL BE CAST OUT. And I, if I am lifted up from the earth, will draw all peoples to Myself.” It is clear Jesus was “ANTICIPATING the cross in these words. He knew the “hour had come” for Him to be “obedient unto death, even the death of the cross” (Philippians 2:8). He also knew that in His death He would be “judging the world that hated Him” and Satan, the “ruler of this world.” The world’s hatred of Him caused them to crucify Him and behind them was Satan who inspired the mob on that fateful day to put Him to death. But they failed to know that by His death they would be DEFEATED. They wanted to do away with Him forever, but instead they will one day be “consigned to Hell forever” (see Revelation 20:10, 11-15). Their condemnation was sealed when Christ died and their sentence will be executed in a coming day based on Christ “overcoming them on the cross.”

Now let’s dwell on Jesus’ words, “And I, if I am lifted up from the earth, will draw all peoples to Myself.”  I believe this refers especially to “all believers being drawn to Him as Savior.” Believers are coming to Christ from EVERY NATION in the world! Now let’s connect this truth with our verse (John 16:33) which reads, “These things I have spoken to you, that in Me you may have peace. In the world you will have tribulation; but be of good cheer, I have overcome the world.” Jesus knew that the world would hate us and persecute us just as they hated and persecuted Him (John 15:18-25). He even knew that some believers would be put to death by those in this world (John 16:1-4). But He tells us to be of GOOD CHEER, for He would give us “His peace” (John 14:27). Even though we will have TRIBULATION NOW, He has “overcome the world” and we are assured of the final victory that we will share with our blessed Lord and Savior. This in turn can “give us victory even now” over the world and Satan as they seek to rob us of our joy and influence us for evil. I will close with a precious passage that speaks to this: “For whatever is born of God OVERCOMES THE WORLD. And this is THE VICTORY THAT HAS OVERCOME THE WORLD—our FAITH. Who is he who overcomes the world, but he who believes that Jesus is the Son of God” (1 John 5:4-5).  (DO)  (619.3)