My sister confronted her husband and he swears it is all to do with the ministry, calls, Bible studies etc. He says she is being ridiculous and it is entirely innocent.
Completely got trapped in a stupid side argument - aka, red herring.
It's not important what the texts are about. What's important is that the frequency of calls is upsetting to the wife.
She needs to pur her big girl pants on and start a real conversation - about what is and is not OK in their relationship. And not get bogged down in trivialities (e.g., what the calls are about).
Any caring, Christian husband would be concerned that his wife is unhappy, that he is the cause of anxiety for her.
A guy in that situation may feel suffocated over "jealousy" - in which case he perhaps shouldn't be married.
In any case, he's putting her down and trying to trump her concerns with his doing God's Will. That needs to be addressed.
She'll either put up with it, or put her foot down. He'll either insist on it, or become more caring of her needs.
Let us know what happens...