I have a question. I took your advice and want to get married. My mum, my wife-to-be, and I are cool with getting married in a Lutheran church. Our bone of contention comes from our best man and woman who are born again, like ourselves. They will not do a wedding at a Lutheran church. They say their teachings are not of Christ. They also look like they want to recruit us to attend their marriage classes. I don’t attend the Lutheran church, but I am getting married there because the pastor at my church is American, and I don’t think he has a license to marry people in this country. The Lutheran church is denominational, but I don’t mind. I know who I am in Christ; nothing can change that. But our best man and woman have this talk of idolatry being done at the Lutheran church. I didn’t know there is so much contention between the Lutheran and the spirit-filled churches. I thought God says we are one. I know I am a freeman (Galatians 5:3-15).
A marriage is not made by the place the ceremony is held. That was one of Paul's points to the Corinthians: "For the unbelieving husband is sanctified by the wife, and the unbelieving wife is sanctified by the husband; otherwise your children would be unclean, but now they are holy" (I Corinthians 7:14). If only marriages in Christ's true church were legitimate, then the majority of the world would not be married. God recognizes all marriage covenants, even the ones made before a justice of the peace in a county courthouse where no preacher is involved.
Your best man and the maid-of-honor are there to be witnesses of your marriage covenant. If they have the mistaken idea that only marriages in their own church are legitimate, then you need to find two people who will serve in the role properly. Tell them they are your first choice, but since they are uncomfortable with your choice of venue, you'll find others so as not to force them to do what they think is wrong (Romans 14:22-23).
Your friends don't understand other religions well. I suspect that they are mixing up Roman Catholicism with Lutheranism. In the Roman Catholic church, there are many images of Jesus, Mary, and saints that are used as places of prayer. Most of the world sees this as a form of idolatry, but the Roman Catholics deny it. Lutherans don't use images in their worship.
Jesus said that his church is one (Ephesians 4:4-6), but that doesn't mean men haven't divided the one true church with their various doctrines. Just because a church claims to be following Christ doesn't mean it actually is. Words are easy to give, but actions often show a difference. See "Cafeteria-Style Religion" and "How a Church Loses Its Distinctiveness."