We are guilty of sin in taking such an oath or making such a vow, and we would be guilty of still greater sin by keeping them. The second Commandment forbids all false, rash, unjust, and unnecessary oaths, blasphemy, cursing, and profane words. A. Blasphemy is any word or action intended as an insult to God. To say He is cruel or find fault with His works is blasphemy. It is a much greater sin than cursing or taking God's name in vain.
Profane words mean here bad, irreverent or irreligious words.
Remember thou keep holy the Sabbath day. By the third Commandment we are commanded to keep holy the Lord's day and the holydays of obligation, on which we are to give our time to the service and worship of God. A. Holydays of obligation are special feasts of the Church on which we are bound, under pain of mortal sin, to hear Mass and to keep from servile or bodily labors when it can be done without great loss or inconvenience. Whoever, on account of their circumstances, cannot give up work on holydays of obligation should make every effort to hear Mass and should also explain in confession the necessity of working on holydays. We are to worship God on Sundays and holydays of obligation by hearing Mass, by prayer, and by other good works.