The comma you've used here isn't wrong, but I don't think it makes the sentence as clear as it could be. That doesn't necessarily mean we should use a semi colon instead; the short answer is that I would use neither.
Let's break down what's happening.
These will be covenants that we decide to be held to, not forced, but encouraged, so that each of us has the opportunity to further mature in our faith.
There are a few reasons why you might employ a semicolon, but the main one is to avoid comma splices. This occurs when two independent clauses are joined together with a comma. Instead you can use a period, or, to preserve the relationship between the clauses, a semicolon. Let's look at the second half of the sentence:
✘ Not forced, but encouraged, so that each of us has the opportunity to further mature in our faith.
This is a sentence fragment on its own. "Not forced, but encouraged" has no subject, and can not stand alone as an independent clause; therefore a semicolon is probably not the right choice.
I think the easiest way to go about this would be to look instead at what the commas are doing in the original draft. Commas can also do a bunch of different things, but in this case they are being used to set off a parenthetical element. A parenthetical element is part of the sentence that supplies some extra information but can be removed without making the sentence ungrammatical or changing the meaning entirely. Using parentheses instead, this becomes much clearer:
✔ These will be covenants that we decide to be held to (not forced, but encouraged), so that each of us has the opportunity to further mature in our faith.
You can also see that our parenthetical element has a comma in it itself. This is why I feel your sentence is a bit muddled also using commas for the parentheses, and why I would refrain from using them here myself.
This is a totally acceptable way to write this, but in the interest of options I'll also propose a punctuation mark which I am very fond of myself: the emdash. I'll quote two sources below on the use of emdashes, and you may notice one claims they're less intrusive than parentheses and one claims they're more intrusive. I tend to find them less intrusive, but perhaps such things just depend on your reader. In any case, I would personally be most likely to write this sentence as follows:
✔ These will be covenants that we decide to be held to -- not forced, but encouraged -- so that each of us has the opportunity to further mature in our faith.
For more information on emdashes you can check here and here. In this particular context I have used them to replace parentheses.