I've found that kids are not dumb. They know if we're going to follow through or not and so if they know we won't, threatening doesn't work for them. My children were told over the weekend that if they were not ready for school on time yesterday, there would be no Webkins (they just got Webkins for Christmas from my brother) and no Wii (got some games for Christmas too). Well, they were not ready and DH blocked Webkins from the internet and I unplugged the Wii. They knew I'd do it but still didn't obey so .......
Do not let the disrespect continue. If you need to, stop the Bible reading, take your son and put him in another room (maybe put him in his bed?) and go back and continue the Bible reading with your other children. When you are finished with the Bible reading, then it is time to deal with your son. I'd address some Scriptures about obeying your parents and how important God's Word is in our lives in a gentle way. I'd ask him if he had any ideas why he was disobeying not just me but God in his behavior and then ask him how does he think he should act next time. You see, just spanking and threatening does not address the issue. He's 7 - you need to be clear, explain what is going on and then pray with him that God will help him to crave the Word and that He'll help him to behave better the next time. Now you've told him your expectation and GOD'S expectation. Additionally, tell him the punishment for not being respectful during your Bible time, whether it is no TV, a spanking or whatever. But make the punishment believable and if at all possible, tie it to the reading time. Possibly telling him that he cannot sit with you and your other children during that time and that instead, he needs to go to bed early. But whatever you do, FOLLOW THROUGH and be consistent.
The next time he misbehaves, be gentle, be firm and be quick. Do not allow the behavior to continue. Address it NOW and remove him from your presence so that it does not affect the other kids. I think he has your number because there's no consistent discipline and he totally knows he can usually get away with it. Some kids are like that. I had one who I had to NEVER EVER let my guard down. Of course now she's 17 and a wonderful young woman who learned about self-discipline and such because I taught her discipline from me. She's really a good kid even though she was a terror when she was young.
Please let us know how it goes.