Yes, if you work a part-time job, you can still qualify for Social Security and Medicare.
In order to qualify for SS, you need 40 quarters of income, or 10 years' work, in the prior 35 years. Part-time employment that is subject to Social Security withholding qualifies for this. So a secular job will help you get SSI. When you elected not to take SS due to your religious work, it only applied to religious work, it has no effect on secular work.
In order to qualify for Medicare, you need 20 quarters' work, or 5 years.
The IRS considers one quarter to equal to $1,260 this year. So if you make about $5200 this year, you will get the maximum 4 quarters of credit.
I hope this answers your questions! If you have any more, please feel free to ask and I will be happy to answer.
Thanks! Have a great week!