Romans 13:8 Owe no one anything except to love one another, for he who loves another has fulfilled the law.

Proverbs 22:7 And the borrower is servant to the lender.

Exodus 20:15 "You shall not steal."

The scriptural prohibition against stealing means that all debts must be repaid. Getting into debt beyond what can be quickly repaid means that you have an obligation to work for an extended period of time to pay back the lender. That kind of obligation to work to pay back your lender is a form of slavery.

Collateralized debts (e.g., house mortgages) are a way to organize a longer-term debt with minimal risk of defrauding the lender. Extended mortgage terms (10+ years) can be self-enslaving due to the high amounts of mortgage interest you will pay.

By enslaving yourself with debt, you also enslave family and close relations who depend on you. Rather than having a surplus to bless others with, you are in need of charity yourself.