Having a passion for spreading the Love of God is in one sense all that you need but having an understanding of what you want to be about, prepares you to be much better at the job.
A diploma in theology is what helped open my eyes but as much as I value my education it's not the only way to get the knowledge that you need.
I remember when I was much younger, starting to express my passion for evangelism and being told by my elders that I wasn't allowed to do most things because I did not have the theological education.
When I questioned why I needed such education I given many answers, but the one that irritated me the most was "Jesus gave his disciples 4 years of training before he set his disciples loose on the world". "But Jesus is not dead!" I would object.
Can I tell you that tell you that church politics is a fickle thing and if you want to achieve something in a conservative church showing you elders up for their flawed theology is not the way to do it.
But it is true that Jesus, through the Holy Spirit has never stopped teaching his children how to reach the world. More than that the statement about "4 years" is just not true. Jesus put his disciples through an apprenticeship. They were out in the field almost from the very start of Jesus own ministry.
Don't let anybody stop you from telling others about the God you love, no matter how little you know. But because he loves you, you will get educated whether you like it or not if you belong to him and are filled with the Holy Spirit. Because that what the Holy Spirit does.
More than this if you live in a first world country you don't have to go to bible college to get a theological education. There are books, Short courses, Short term mission, your church in a pinch, if you've got good leadership(don't get me started on the poor standard of education offered in our church by those that "are" theologically educated) and now there is the internet.