"I have given my word to the Lord, and I cannot go back on it" †
Difficult passage. Does God want human sacrifice?
Indeed, this passage may not imply he sacrificed her in this way. Wording allows for a consecration away from ordinary use, so she could never marry or bear children. "Burnt sacrifice" = olah = "ascending" literally, and can be metaphorical. But "and" in 11:31 could be "or" anyway in the Hebrew.
In either case, what are the lessons?
1. Biblical interpretation is not always straightforward. Often to understand a passage it needs the rest of the Scripture, as well as the Church's wisdom, including scholarship.
2. Simple practical advice: Shut up. "He that keepeth his mouth keepeth his life: but he that openeth wide his lips shall have destruction." Proverbs. 13:3 etc. Many words can result in much error and pain. Pause and reflect, do not mistake a degree of passion for a degree of certainty.
3. Make the words you do say have impact by letting the rest of your life be an epiphany, a showing forth, of the light of Christ.†