That is why he voluntarily took the human form of Jesus Christ so that he would be able to suffer and die as a mortal human being. Only through this incredible act of love could mankind have any chance of salvation and eternal life. The very last thing that Our Lord would want is not to be able to complete his mission for his Father. So Jesus was not worried about any of these things. He was worried about something far greater than that. What he was worried about was being separated from God the Father.
And the reason that Jesus was going to be separated from his Father was because he was about to have every single sin that mankind had ever committed, or would ever commit, laid directly upon his soul. He knew that he was going to be carrying all the sins of the world, and he realized that these sins would be the very reason why he would be separated from his Heavenly Father.
2 Corinthians 5:12 "For He made Him who knew no sin, to be sin for us, that we might become the righteousness of God in Him."
He knew that his Father hates sin, that God won't even be in the presence of sin, that sin is ungodly and wicked, and that sin is the actual rejection of God. And most importantly, he knew that sin separates the sinner from God. You cannot be in sin and at the same time be with God. So Jesus knew that once all of mankind's sins began to be transferred over to him, then he would be separated from his Father. The sins of mankind that Jesus was going to carry was what was going to alienate and separate him from his Father, for the very first time in all of eternity.
As the crucifixion of Jesus Christ started, the very first sins began to pile up on his soul. Jesus, for the first time in all of eternity felt the same separation from God the Father that any person feels who is living in sin and who is outside the grace of God. For the first time in all of eternity there was a complete separation, a complete alienation from his heavenly Father. The sins of all mankind that Jesus was carrying caused God the Father to separate himself from his Son. That is why as Jesus hung on the cross, in utter loneliness, he pleaded with his Father to comfort him. He screamed out asking why his Father had forsaken and abandoned him. Matthew 27:46 "And about the ninth hour Jesus cried out with a loud voice, saying, My God, My God, why have You forsaken Me?"
Jesus knew the answer to that question, because Jesus understood that the sins that he was carrying for all of mankind was why he had been separated from his Father. Jesus also knew that his mission on earth was completed. And he also knew that it was successful. Because as Jesus took his very last breath he uttered those final three words of his earthly life. Those three words that told his Father, and told the entire world, that the purpose for which the Son of God came here for was indeed successfully completed. John 19:30, "It is finished", and bowing his head he delivered up his spirit.
These three words were not the words of defeat, rather they were the words announcing a glorious victory.
Other reasons why Jesus suffered so very much and began sweating drops of blood in the Garden of Gethsemane
Besides knowing that he was going to be separated from the Father because of the sins that he was soon going to be carrying, there were other things that were happening to Jesus that was causing him great heartache and emotional distress. For instance,
1) The entire Jewish Nation that he came to save had turned its back on him.
2) One of his very own, at that exact instant was in the process of betraying him.
3) His greatest supporter was soon going to deny him over and over and over.
4) This is the one and only time that he really needed his friends support and comfort, and all they could do was keep falling asleep.
5) Jesus found himself to be utterly and completely alone. There was not a single person on this entire planet who stood by his side. Not a single person who spoke up for a fellow human being. Not one person gave comfort or spoke words of encouragement.
6) He knew that all his friends would very soon be running away from him as fast as they could.
7) He knew that soon he was going to go through extremely horrible pain and suffering.
His Father's heart must have been breaking to see all this happening. He knew that these things were so very painful for Jesus, so his Father sent an angel to the garden of Gethsemane, to give him the only comfort he would ever again receive while in his mortal human body.
Luke 22:43, "Then an angel appeared to Him from heaven, strengthening Him. And being in agony, He prayed more earnestly. Then His sweat became like great drops of blood falling down to the ground."