One does not need to dive into the Greek to understand clear cut passages. Sometimes it helps and can be quite beneficial, but on clear cut passages like Gal. 5:3-4, it’s pretty plain. It refutes the false doctrine of OSAS (the impossibility of apostasy), but as always, people want to say it doesn’t mean what it says and it doesn’t mean what it means. As stated in John 8:32, we shall know the truth, can prove all things (1 Thess. 5:21; 1 Peter 3:15). Jesus expected people to understand Him (Mk. 7:14). Regular people can accomplish this (2 Timothy 3:16,17; Acts 17:11; Ephesians 5:17). The Bible was written for fishermen, farmers, tent makers, and the poor to be able to understand.
A lot of times, people who go to the original language to prove something ends up proving something that cannot be proven in the scriptures. Or, they use a word or meaning of one that gives a different “spin” on what the original meaning has. In other words, their goal was to establish what cannot be found in the English texts. Any practice that can only be verified by studying the original Greek should be immediately suspect.
Without learning Greek or Hebrew, the average individual can learn the meaning of Bible words in three different ways: (1) Context, (2) Translations, and (3) Additional passages.
Romans 5:20-21 clearly states that God's grace reigns through righteousness. Righteousness is in the saving message of Christ— the gospel, clearly stated in Romans 1:16-17. As a result, falling from grace (Gal. 5:3-4) entails losing access to the gospel's sin-cleansing blessings! In other words, all individuals who attempted to revert to the weak and beggarly features of apostate Judaism (Galatians 4:9), although having been baptized into Christ (Galatians 3:26-29), had ceased to walk in the light and began to walk in darkness (1 John 1:5-10). They needed to repent and pray (Acts 8:22). The erring brethren of the church in Galatia or elsewhere could return at any time, but they had to do so in the manner prescribed by God in the gospel.