A minister who wishes to be exempt from social security/Medicare tax must file a Form 4361 with the IRS for approval. Before your application can be approved, the IRS must verify that you are aware of the grounds for exemption and that you want the exemption on that basis.
When your completed Form 4361 is received, the IRS will mail you a statement that describes the grounds for receiving an exemption under section 1402(e). You must certify that you have read the statement and seek exemption on the grounds listed on the statement. The certification must be made by signing a copy of the statement under penalties of perjury and mailing it to the IRS not later than 90 days after the date the statement was mailed to you. If it is not mailed by that time, your exemption will not be effective until the date the signed copy is received by the IRS. So it is extremely important to complete this last step, or you will not be exempt. Once the IRS approves it, you will receive a copy marked approved.
The grounds for opting out are not economic or non-religious, but are based on opposition to the acceptance of public insurance with respect to services performed as a minister. It should be noted that the opting out only applies to ministerial earnings. A minister is not being inconsistent in accepting SS or Medicare benefits from non-ministerial earnings.