Through Thick (=51) and Thin (=51)

 

T+H+I+C+K = 51 = T+H+I+N

“Through perils both of wind and limb, Through thick and thin she followed him” - Samuel Butler
 
"Men do fancy a necessity [of holiness] where there is none, yet that will carry them through thick and thin." - Richard Baxter

"'Through thick and thin' is one of the English language's older expressions and one that has maintained its figurative meaning over many centuries. It is venerable enough to date from the times when England was still a predominantly wooded country, with few roads and where animals grazed on what was known as wood pasture, i.e. mixed woodland and grass. The phrase originated as 'through thicket and thin wood', which was a straightforward literal description of any determined progress through the 'thick' English countryside." - The Phrase Finder