What are these characters? (Characters identified: 牧者所愛)
The first three characters are indeed 「牧者所」, with 「牧」 written with a corrupted 「攵」 which appears as 「文」. The last character is a reshuffled 「」, which in the current script is written as 「愛」.

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「愛」 (Baxter-Sagart OC: /*[q]ˤə[p]-s/, [benevolent] love) was originally written as 「㤅」, comprised of semantic 「心」 (heart) and phonetic 「旡」 (/*[k]ə[t]-s/).
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「夊」 was added later for no particular functionality. This was perhaps stylistic, and happened in several characters right below a component with the shape of a person. For reference, 「旡」 depicts a kneeling person with an open mouth.
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「旡」 was later corrupted into 「⿱爫冖」, forming 「愛」. Sometimes, 「心」 and 「夊」 were also shuffled around; if 「心」 is moved to the bottom left, it is written as 「忄」.

The character in question,

retains the non-corrupted 「旡」
　
and shuffles 「心」 to the bottom left.
　

References:

小學堂

字形演變
異體字表


漢語多功能字庫
中國社會科學院考古研究所《殷周金文集成》