Oh, well, what I just posted on the Hermeneutics thread will apply here:
Harmonizing all truth/GW requires the following:
1. Employing "both-and" thinking or reasoning rather than "either-or" when it is helpful and does not contradict obvious moral teachings.
2. Preferring synonyms over antonyms when logically and morally possible (no false equivalence).
3. Striving for agreement regarding the essential issue (God's requirement for salvation) instead of being quick to quarrel.
4. Triangulating from undebatable doctrines in order to interpret problematic passages.
Also, the point of the Key OT Teachings thread is to note OT Scripture related to the NT teachings.
Regarding "God doesn't change", we should note that there are two main ways God/Christ is encountered:
1. General revelation, which includes meditating on the natural world or God’s supernatural work and moral conscience. Paul said men are without excuse, both because God’s eternal power and divine nature (love) are manifested by creation (Rom. 1:20), and because a proto-gospel has been proclaimed to everyone under heaven implicitly or in pre-NT foreshadowings (Col. 1:23, Rom. 10:13-18, Gal. 3:8). He also taught that all normal humans have an inner conscience or “common” sense (Rom. 2:14-16), which manifests morality or a moral Authority in every culture. Thus, sinners have no excuse for not seeking God’s salvation or being truthseekers (Matthew 7:7, Hebrews 11:6).
2. Special revelation (1Pet. 1:8-12), which refers mainly to divinely inspired NT teaching regarding God’s history of salvation. Again, the Parable of the Talents indicates that souls are saved via faith in God/ Christ as revealed (cf. 1Cor. 10:1-5). Truthseekers around the world in all times are pilgrims at various places along the road of life, and all true roads eventually lead to the Way to eternal life in heaven (John 14:6, Acts 24:14, Phil. 2:10-11). All truth leads to One Way.
Hope you consider this old man's discussion to be rich!