You don’t have to be a perfect Muslim in order to talk about Allah Most High and His messengers and their messages. There are numerous reasons for this.
Firstly, spreading Islam is a good deed like any other good deed. A non-practicing Muslim is not stopped from doing good deeds like charity and so on, in the same way he should not be stopped from giving D’awah. Secondly, in Islamic history you will find many examples of how even the sincere words of a sinful person helped others by the grace (fadhl) of Allah. Lastly, if being a perfect Muslim was a condition of spreading Islam then I don’t think anyone would have a chance of doing the work of D’awah, since no one is on the level of perfection that the Prophet Muhammad (Allah bless him and give him peace) possessed.
As Muslims we should remember this narration (hadeeth) if we ever feel arrogant and think we are free from sins:
“All the children of Adam fall into sin, and the best of sinners are those who repent.” [Tirmidhi]
So I hope that this has helped clarify that talking about Islam is not restricted to pious Muslims, but is actually something we can all do. You don’t need to talk about lengthy fiqh issues, you can leave that to the ones who have gained licenses (ijaazah). Instead focus on talking about the greatness of Allah, talk about what you find inspiring about Islam, or a story that inspired you and by passing on what you know, it will help others in ways you can’t imagine.
It’s only a matter of beginning to give D’awah. There are many people I know who due to continuously giving D’awah over a period of time, find it so easy to talk about Islam no matter who is in their presence. It’s become a habit to them. One other thing noted about these individuals is that they are always trying to learn more about Islam, and that is definitely a quality worth having in order to excel in the work of D’awah. Another quality seen amongst them is humility, and the ones that actually are successful in this work are humble.
Now, although being a perfect Muslim is not a condition for calling people to Allah, this however does not mean that we should take a back seat from striving for perfection or not trying to improve ourselves. As Muslims, it is our duty to be the best we can in this life. It is mentioned in the second verse of Surah Al-Mulk that Allah created life and death so that He could test who among us is the best in their deeds. May Allah help us and inspire us to be good and to do good. Aameen
And Allah alone gives success.