Jerry Johnson, the President of National Religious Broadcasters (NRB) which has more than 1400 members, was speaking after he and a thousand other evangelicals attended a meeting with Donald Trump in New York last week.
The meeting was the biggest example of Christian-specific exposure Mr Trump has had since announcing he would run for the presidency last year, and many have viewed the response from the conference as a signal of Evangelical opinion across the US towards him.
The group refused to hold a vote on whether to endorse Donald Trump on the day, wanting to see what else the Republican candidate says and does in the future first.
Mr Johnson also said Donald Trump has "a lot of growing to do" in his relationship with God.
The Republican candidate has received criticism from some Christians for his previous views on social issues such as abortion and gay marriage and for saying he has never explicitly asked God for forgiveness.
His faith has also been questioned after remarks he has made towards Mexicans, women and the disabled.
However, Donald Trump told pastors and church leaders at the conference that he owes Christianity "so much".
At the conference, Donald Trump announced he would appoint a special Evangelical Advisory Group to advise him on issues important to Christians.
He also pledged to appoint a conservative set of Supreme Court judges who would be more likely to rule in accordance with Christian values and scrap a rule which stops Christians from lobbying politicians without losing their tax-exempt status.
Some Christians have argued the rule, called the Johnson Amendment, is unconstitutional as other charities are able to lobby government while maintaining their tax-exempt status.
In an exclusive interview, Jerry Johnson told Premier: "In my case, and I think for most people, this is a process - we're working through it. We're going to see how he develops, we're going to see the other issues that come up.
"What does he say next week? Because he's always got a surprise. This isn't a done deal.
"To be frank, it's hard to judge another person's faith. When they say they're a Christian, you don't want to oppose that.
"But he's certainly got a lot of growing to do. We all do, though.
"He says: 'I've got your back, I'll look out for you'.
"He may not talk about faith the way we talk about faith - he's lived in a different world there in New York City.
"I think Christians have felt like we were the only minority that can be criticised and critiqued and indeed censored, and he says: 'that's over - if I'm elected, I'm going to look out for your interests'."
Listen to Premier's Aaron James speaking to Jerry Johnson: