A man who was completely innocent, offered himself as a sacrifice for the good of others, including his enemies, and became the ransom of the world. It was a perfect act.
A principle is the expression of perfection, and as imperfect beings like us cannot practise perfection, we devise every moment limits of its compromise in practice.
A vow is a purely religious act which cannot be taken in a fit of passion. It can be taken only with a mind purified and composed and with God as witness.
All compromise is based on give and take, but there can be no give and take on fundamentals. Any compromise on mere fundamentals is a surrender. For it is all give and no take.