@Josheb
Your post included in my reply plus my reply is way over 1,000 characters, so I am sorry, but I cannot include your entire post in my reply.
Thank you, and I appreciate your giving attention to this. I have to break this response into two sections to fit the platform limitations.
I notice that you use a New Testament word in 1 Peter 3:21 that appears to be used only one time in the New Testament, and more often translated "answer" than pledge.
I honestly have no idea what went through the minds of those constructing the WCF, nor what passages of Scripture they had in mind when they wrote the word "pledge." Maybe there are some commentaries by participants who would shed their perspective on this.
As you have raised the question about "pledge" in the Scripture, though you limited it to the single New Testament usage of the word, Bible translators have used the word "pledge" many, many times in the Old Testament. I mean 22 times in 21 verses.
Here is the Blue Letter Bible Link:
https://www.blueletterbible.org/search/search.cfm?Criteria=pledge&t=KJV#s=s_primary_0_1
To save time, here are the verses. Count how many times they use pledge as something that will be delivered when conditions are met:
[Gen 38:17-18, 20 KJV] 17 And he said, I will send [thee] a kid from the flock. And she said, Wilt thou give [me] a pledge, till thou send [it]? 18 And he said, What pledge shall I give thee? And she said, Thy signet, and thy bracelets, and thy staff that [is] in thine hand. And he gave [it] her, and came in unto her, and she conceived by him. ... 20 And Judah sent the kid by the hand of his friend the Adullamite, to receive [his] pledge from the woman's hand: but he found her not.
[Exo 22:26 KJV] 26 If thou at all take thy neighbour's raiment to pledge, thou shalt deliver it unto him by that the sun goeth down:
[Deu 24:6, 10-13, 17 KJV] 6 No man shall take the nether or the upper millstone to pledge: for he taketh [a man's] life to pledge. ... 10 When thou dost lend thy brother any thing, thou shalt not go into his house to fetch his pledge. 11 Thou shalt stand abroad, and the man to whom thou dost lend shall bring out the pledge abroad unto thee. 12 And if the man [be] poor, thou shalt not sleep with his pledge: 13 In any case thou shalt deliver him the pledge again when the sun goeth down, that he may sleep in his own raiment, and bless thee: and it shall be righteousness unto thee before the LORD thy God. ... 17 Thou shalt not pervert the judgment of the stranger, [nor] of the fatherless; nor take a widow's raiment to pledge:
[1Sa 17:18 KJV] 18 And carry these ten cheeses unto the captain of [their] thousand, and look how thy brethren fare, and take their pledge.
[Job 22:6 KJV] 6 For thou hast taken a pledge from thy brother for nought, and stripped the naked of their clothing.
[Job 24:3, 9 KJV] 3 They drive away the ass of the fatherless, they take the widow's ox for a pledge. ... 9 They pluck the fatherless from the breast, and take a pledge of the poor.
[Pro 20:16 KJV] 16 Take his garment that is surety [for] a stranger: and take a pledge of him for a strange woman.
[Pro 27:13 KJV] 13 Take his garment that is surety for a stranger, and take a pledge of him for a strange woman.
[Eze 18:7, 12, 16 KJV] 7 And hath not oppressed any, [but] hath restored to the debtor his pledge, hath spoiled none by violence, hath given his bread to the hungry, and hath covered the naked with a garment; ... 12 Hath oppressed the poor and needy, hath spoiled by violence, hath not restored the pledge, and hath lifted up his eyes to the idols, hath committed abomination, ... 16 Neither hath oppressed any, hath not withholden the pledge, neither hath spoiled by violence, [but] hath given his bread to the hungry, and hath covered the naked with a garment,
[Eze 33:15 KJV] 15 [If] the wicked restore the pledge, give again that he had robbed, walk in the statutes of life, without committing iniquity; he shall surely live, he shall not die.
[Amo 2:8 KJV] 8 And they lay [themselves] down upon clothes laid to pledge by every altar, and they drink the wine of the condemned [in] the house of their god.
Again, none of us know what was going through the minds of those who authored WLC #20. You raised the point that they would look to Scripture. If they did, then the vast majority of the uses of "pledge" would mean something offered when conditions were met.
Honestly, don't you think, in light of how often "pledge" is used as I understand it, that the case could be made that bias exists in reading "pledge" as anything but something offered when specific conditions are met.
Judah would get his pledge - his ring - back when he met the conditions of paying for the services of the "harlot." The garment given as a pledge would be restored when the sun goes down ... the list of Biblical uses of pledge as I understand it, seems to me to be overwhelming.
Would you agree, or disagree?