There has been scholarly discussion over the years on what exactly did Jesus come to do and accomplish while on earth. Some have suggested that Jesus was only a mere man and prophet who came with a message, but this message didn't have any eternal credence or consequences.
I would like to propose a different yet biblical point of view. The Bible in Christendom is considered our "first source" when it comes to unpacking what Jesus came to do and who He was. Let me explain.
The person who says Jesus was only a mere man and prophet must be getting their information from some other source than the Bible. This would be considered a "second source." As we ask the question what did Jesus really come to do, first source must be examined as our primary resource. The Bible begins telling us how all things came into existence (Gen 1:1), how God created and formed man out of the dust of the ground (Gen 2:7), then quickly exposes how sin entered the world (Gen 2:9, 17, 3:22). This sin put enmity between God and man (Gen 3:15) and the first animal sacrifice took place (Gen 3:21) to cover Adam and Eve's nakedness and sin (Gen 3:7, 3:11). Since the fall of man, animal sacrifice continues as a form of devotion and worship to God (Gen 8:20, 22:2, 31:54, 46:1, Exodus 5:3, 8:8, etc.).
The Bible continues to express how sin can only be covered or taken away by sacrifice and bloodshed in Lev 9:7s
Moses said to Aaron, 'Come to the altar and sacrifice your sin offering and your burnt offering and make atonement for yourself and the people; sacrifice the offering that is for the people and make atonement for them, as the Lord has commanded
Animal sacrifice, or better known as atonement, was only sufficient for a limited time. Each year the High Priest made sacrifice for his own sin then sacrificed for the entire nation of Israel (Hebrews 5:1-4). Animal sacrifice was repeated year after year until Jesus' sacrifice was made on the cross for the sins of the entire world (John 3:16).
The Hebrew writer elaborates more on the sacrifice Jesus made which was more superior or greater than any animal sacrifice for sins. He continues in Hebrews 9:11-13
11 But when Christ came as high priest of the good things that are now already here, he went through the greater and more perfect tabernacle that is not made with human hands, that is to say, is not a part of this creation. 12 He did not enter by means of the blood of goats and calves; but he entered the Most Holy Place once for all by his own blood, thus obtaining eternal redemption. 13 The blood of goats and bulls and the ashes of a heifer sprinkled on those who are ceremonially unclean sanctify them so that they are outwardly clean.
Therefore Jesus came to redeem people from their sin by sacrificing Himself on the cross. Like I mentioned this was more of a theological way to provide insights on what Jesus came to do, but I would also like to provide an answer by quoting Jesus Himself. Lets focus on a couple of the passages in the bible when Jesus Says "I have come." In Matt 5:17 Jesus says:
Do not think that I have come to abolish the Law or the Prophets; I have not come to abolish them but to fulfill them.
Luke 24:44 Jesus reminds His disciples of what He had spoken about earlier in Matthew 5:17 about Him fulfilling everything that was written by the Prophets, in the Law, and Psalms.
In conclusion, Jesus says He came to fulfill everything that was spoken about Him. The culmination of this fulfillment came by His substitutionary death on the cross so that by faith in Him anyone can have eternal life. John 3:16