What does one need to “work for” in regards to eternal life in John 6:27?
Answer: We must hear, believe, repent, confess, and be baptized. We must then live godly lives.
This is actually very simple, and it gets much easier over time. Just as Perry mentioned, belief in Christ is "a work":
John 6:28-29: "Therefore they said to Him, 'What shall we do, so that we may work the works of God?' Jesus answered and said to them, 'This is the work of God, that you believe in Him whom He has sent.'”
All of the conditions of salvation are "works."
Christ's "Law of Liberty" or "Royal Law" is comprised of the essential works of:
1. Belief in Christ (Jn. 6:29);
2. Repentance from sin (Acts 26:20);
3. Confession that Christ is Lord (Matt. 10:32);
4. Baptism or immersion in pure water, and,
5. Sustained obedience to God.
James tell us the following: "Faith without works is dead" (Jas. 2:26). (5) above includes worship consisting of prayer, communion, songs, and biblically-founded preaching. It also includes studying the Word of God (immersing oneself in the Holy Spirit).
The rest we finally enter, our Promised Land in Christ, is an eternal rest with God, the New Testament sabbath. These all result in the following conditions:
Salvation, Forgiveness, Justification, and Newness of life in Christ.