Salam, Saladin.

I pray this finds you well.

Due thanks be to Allah, majestic in His praise. I am truly happy with your conversion. May Allah enlighten your heart and strengthen your faith and grant you His love and good pleasure.  

Before going directly into answering your question I would like to share two important ideas related to existence and fate in general. I would also like to comment on moral issues related to Muslims in general. These will then directly link to the answer to your question.

Between the Unknown and Reality

There are ontological axioms that Allah Most High states with regard to each and every life, no matter how much agony one goes through.

First, as many scholars read the totality of our beings, Allah Most Wise has created, appropriated, and masterly sustained our beings in such a way that not a single change in our lives can make the totality of  our being better for any of us.

Hence the insightful aphorism, "If you knew the Unknown, you would choose reality" Translated into the state of affairs of each of us, this means that every human is created into the best and most suitable life, in accordance with their capabilities, circumstances, and — above all — ultimate destiny.

You are no exception. 

No Burden Greater Than You Can Bear

Allah Most High says in the Qur'an what means the following:

*{Surely We have created everything according to a measure. And Our command is but one, as the twinkling of an eye.}* (Az-Zumar 39: 49–50)

*{On no soul doth Allah place a burden greater than it can bear.}* (Al-Baqarah 2:286)

This means that each of us is destined to only what we can bear. In other words, the occurrence of something means that it is bearable.

That said, I would like to assure you that your situation — complicated, emotionally charged, fragile, and sensitive as it may be — is bearable, and in fact, it can be handled with ease.

Respecting Parents

Of course, dealing with one's parents with due decency and benevolence, irrespective of their religious beliefs, is not a mere Islamic injunction; it is actually a pivot of our religion.

Suffice it to say that dealing with parents beautifully or excellently is the single command in the Qur'an that Allah Most Sublime directly couples with worshiping Him solely.   

We read in the Qur'an what means the following:

*{And your Lord has commanded that you shall not serve (any) but Him, and goodness to your parents. If either or both of them reach old age with you, say not to them (so much as) "Ugh" nor chide them, and speak to them a generous word.}* (Al-Israa' 17:23)

An Atheist Father's Ridicule

Now, with regard to your question, dealing with your strictly atheist father and his continuous insults to Islam should be done in light of all that was said above.

You are perfectly capable of dealing with your destined and wisely proportioned situation. That's your test. Defending Islam is of course a must on your part, but there are a few words of advice here.

The first thing I would advise you to do is to pray to Allah earnestly for help with your situation. He is the Commander of everything and everyone; under His command are hearts of all humans. The best time would be late at night before dawn.

Second, I guess the most important thing that you should do at the moment is to strengthen your friendship with your father, irrespective of you wanting to defend Islam. Be sincere about it.

Befriend your father for the sake of wanting to do so, not as a mere instrument to get him to understand or believe in Islam. Put more effort into going out with him.

Little by little, develop a warm and pleasant connection that allows you to discuss everything with him: daily matters, politics (especially since you are originally Palestinian), interests, hobbies, and the like.

This is the best way in the long run, not only for you to grow closer to your father but also for him to get to see the beauty and genius of Islam, directly through seeing how a defender (if you continue to hide your conversion) or believer actualizes it in his dealing with his family.

This is the Prophet's way when it comes to family relations, friendship, and so forth. This is also the best way for your father to start listening to you on all matters without excluding Islam.

Understanding Atheism as a Faith

I also believe that you should start with establishing an understanding with your father in relation to the origin and nature of atheism.

After all, it is a belief that there is no God. Like all beliefs, it should show mutual respect to all other beliefs, as it is a man-made religion and should not be made into atheist fundamentalism.

To know more about atheism as a faith — its components, evolution, and scientific ethos — I highly recommend to you these audio tracks by Sheikh Nuh Keller. I truly believe they will help establish a good intellectual background when dealing with your father.  

The Prophet's Way: Respect All Faiths

The most important advice is simply to uphold the highest level of manners. As Sheikh Hamza Yusuf, a prominent American convert and Islamic scholar, points out, it is never reported anywhere that the Prophet insulted or ridiculed — not even once — any belief whatsoever.

Although, as I can see from your question, you are going so far as to keep your conversion a secret in order not to offend your father, just make sure that your manners are your most important tool in dealing with him.

What this means is that, through your good manners, try to always instill in him the idea of respecting and speaking well of all religions and faith choices, not just Islam. Make your stance, at least in the beginning, that of respecting all faiths without exception.

Keep in mind that normally fathers do not take advice from their children even when the latter are absolutely right, a reality that we all have to deal with. I would say make your focus to influence your father through your manners and not your arguments, no matter how sophisticated and wise they are.

This does not mean that you should not be thoughtful or that you should not put some effort into getting your father to know and understand Islam in its own terms.

The thing is that you and your manners should be a vehicle for your father to learn about Islam, perhaps through igniting his interest and letting him find out about it, even from someone else.

Away from the misconception that Islam was spread by the sword, if one traces the history of the spread of Islam, one will find out that the main reason for it was actually not the work of scholars; after all, the majority of Companions were not scholars.

Nor did Islam spread through economic influence and worldly benefit as a way to attract new followers.

The largest Muslim populations in Africa and Asia — including that in Indonesia, the largest Muslim country in the world — came to Islam through their attraction to the manners of early Muslim travelers and traders they dealt with.

Through their spiritual works and discipline, all people could see and appreciate the light in their faces. This is what attracts people to Islam.

Good luck with your endeavor and keep in touch.

Salam.

Useful Links

After Conversion: Approaching My Atheist Mother

When the Light of Faith Approaches...

When the Light of Faith Approaches... (Another Answer)

Parents' Rights in Islam

Embracing Islam … and Parents Who Object

Embracing Islam in Daily Life

Kindness to Non-Muslim Parents

Showing Kindness to Parents

About to Convert

About to Convert, Concerned About My Family

Convincing Someone to Believe

New Converts and Their Parents

I Need to Be Convinced!