Gathas - Hymns of the Zoroastrian Faith

Gatha Yasna 30
O ye, mindful to learn, I proclaim to you this message,
Unheard as yet by those who are destroying the
 civilization of the Righteous,
 with evil ways of the Spirit of Untruth,
The message, most welcome to Thy followers
 dedicated to Thee, O Mazda!
The hymn or gatha starts off by Zoroaster declaring that he is about to announce the teachings about the Ahuras.  This hymn present some of the major central themes of Zoroastrianism. He continues on by informing the audience or followers to listen to his teachings with "illumined judgement", enlightened mind and decide how one should choose a way of life, good or evil. Choice is fundamental to the faith. It is one's choice to choose either the good "path" or the evil one. Humans have free will, they must choose, and bear it's responsibility or consequence. The subsequent verses talk about basically the fateful alternatives to one's decision. It talks about the doctrine of Good and Evil. Zoroaster talks about how every human being had to choose between the good and bad alternative in every situation in life. He says, humans will choose good because of our Rightmindedness. But Evil is chosen, it is in state of deception. Ultimately, the evil-doers will perish while the good-doers will please Ahura Mazda and find their place in heaven.
Gatha Yasna 18
This gatha talks people's choices and their consequence of picking that choice. These verses deal more with retribution and salvation. The search for truth is important as mentioned in this gatha and wisdom seems to be an admirable trait. As it says,
Long suffering for the doer of Evil, and bliss
for the follower of Truth,
Zoroaster talks about that the righteous humans should make this perfect this world. These verses talk about the humans who choose the path of good, will find their place in heaven while the evil-doers will burn and suffer forever.
Gatha Yasna 33
This particular hymn seems more personal. The verses are addressed to Ahura Mazda. Zoroaster states that "The Ratu (Judge) shall deal perfect justice to all;", in other word, everyone will get what they want. Humans which oppose evil-doing, whether just thinking about it or speak against it, are in good standing with Ahura Mazda. This gatha also explains that anyone, regardless of their social standing, who is good will be accepted into Heaven. The subsequent verses are an appeal to the Ahura. He says,
I, who as Thy steadfast priest, have learned the
straight path of Asha (Truth and Righteousness),
He prays to be blessed with Ahura Mazda's vision and consultation with him because he has chosen the "good path" of "Truth and Righteousness". Zoroaster wants Ahura Mazda to come to him and for his message of good-doings be spread all around.
Gatha Yasna 25
The author, Zarathushtra, states in this last hymn that he is dedicating himself and his life to Ahura Mazda. Zoroaster wishes to be a good person and appeals to Ahura Mazda for his help in becoming righteous. He wants courage and have the ability to see the truth. In these verses, it also seems like that the author desperately wants to go to Heaven.  He hopes that his way of living his life, being devoted to him, is good enough for Ahura Mazda. Zoroaster asks for Mazda's guidance in being a good person and also attaining Heaven.