For one thing, the claim that Zoroastrianism is perhaps the oldest monotheistic religion and that it had an influence on Judaism, Christianity, or Islam is simply not true. While Zoroastrianism is credited to having its origins in the 6th century BC, it only enters recorded history in the 5th century BC. This is in contrast to the Bible, where most historians and scholars put the writing of the Pentateuch (Genesis-Deuteronomy written by Moses) between 1446-1406 BC during Israel’s wanderings in the desert. This means the Old Testament pre-dates the Avesta (official religious text of Zoroastrianism) by close to 900 years.
Secondly, Zoroastrianism states that active participation in life through good thoughts, good words, and good deeds is necessary to ensure happiness and to keep chaos at bay. There are various religious rituals that must be observed and a variety of acts and deeds to be performed to ensure salvation. This is in stark contrast to Christianity which teaches that Christ is the only way to salvation (John 14:6) and that our salvation cannot be earned (Ephesians 2:8-9). This is the unique difference between Christianity and all false religions. In Christ, salvation is a free gift from God apart from works which save no one (Romans 3:20, 28). All other religions require works of some kind to appease God. Thankfully, our Bible is crystal clear on salvation, how to receive it, what is true, and what is not.