<動詞の辞書形> + がよい ― How is this allowed?

Question

I've come across this form many times in my Japanese Bible. The meaning is quite obvious based on context, and seems to be one of the following: ～べきです, ～ほうがいい, ～なさい, or ～ように (let it be ～).

Here are a few verses with this form:

• 神を[畏]{おそ}れる人は皆、聞くがよい...　―　詩編　６６編１６節　／　Come and hear, all who fear God... - Psalm 66:16
• イエスは、「友よ、しようとしていることをするがよい」と言われた。すると人々は進み寄り、イエスに手をかけて捕らえた。　―　マタイによる福音書　２６章５０節　／　And Jesus said to him, “Friend, do what you have come for.” Then they came and laid hands on Jesus and seized Him. - Matthew 26:50
• イエスは、「さあ、あなたがただけで人里離れた所へ行って、しばらく休むがよい」と言われた... －　マルコによる福音書　６章３１節　／　And He said to them, “Come away by yourselves to a secluded place and rest a while.” - Mark 6:31
• しかし、たとえわたしたち自身であれ、天使であれ、わたしたちがあなたがたに告げ知らせたものに反する福音を告げ知らせようとするならば、呪われるがよい。　－　ガラテヤの信徒への手紙１章８節　／　But even if we, or an angel from heaven, should preach to you a gospel contrary to what we have preached to you, he is to be cursed! - Galatians 1:8

How is this form "allowed" to exist without a こと／の following the verb? Is this only a literary written form or something? Because I've never seen this form anywhere except my Bible.

Answer 1

That structure came from classical Japanese (文語), which had been used in formal writing until just after WWII. Technically those are not 辞書形 (終止形), but 連体形. In classical Japanese, the 連体形 of a verb can work as a noun, like 連体形 + の/こと in modern Japanese (口語).

Answer 2

Constructions like 聞くがよい are a command or strong suggestion: "Listen"/"You should listen". On the other hand, if you add の or こと after the verb, I think it becomes a more broad/general statement: "It is good to listen". Maybe it could achieve approximately the same effect, but at the very least I think there's a big difference in the strength of the command/suggestion.