'וכתבת על האבנים את כל דברי וגו, for when they were now sworn at Mount Gerizim and Mount Eyval the Torah was present before them in written format, and they were sworn to keep its commandments.

'אלה יעמדו לברך וגו, according to the plain meaning the tribes mentioned forthwith were to confirm what the Levites said by answering Amen. The Levites, when pronouncing the respective blessings or curses, would face Mount Gerizim when intoning the blessings, and Mount Eyval when intoning the curses. (Sotah 32)

ושם בסתר, there are a total of 12 “curses” corresponding to the 12 tribes, all of the sins mentioned in them being of the type that one commits in private, when one is unobserved and no witnesses are present. I will explain all of them. There are only two of these which are sometimes committed in private and sometimes in public. These are idolatry and striking one’s fellow Jew. This is the reason that the Torah mentions the word בסתר specifically in connection with thee two sins that are listed here. The reason is that for sins committed in public there is no need to utter a curse as people sinning in public are not frightened of the curses either. Not only that, the court has a chance to deal with crimes/sins committed in public. This is the message in 29,28 הנגלות לנו ולבנינו עד עולם, we are forever obligated to deal with publicly committed offenses. Only when crimes are committed in secret do we leave punishment of the sinners to G’d, i.e. הנסתרות לה' אלוקינו, “secretly committed sins are left to G’d to avenge.” (same verse) This includes the whole range of punishments to which the sinner had made himself liable, not only for sins carrying the death penalty. You will note that the Torah does not write ארור שוכב עם אשת רעהו, as normally when one enters another’s house this does not go unobserved. Sleeping with one’s mother-in-law, however, is different, as both parties usually dwell in the same house. (verse 23). Insulting father or mother (verse 16) is something normally done in one’s parents’ home, where strangers are not present. The same is true of someone moving boundaries in the field; (verse 17) it is done at night away from prying eyes. If the one doing it were to do it in full view of his neighbour, surely he would be challenged. The same applies to misdirecting the blind, (verse 18) or someone sleeping with a beast (verse 21). Naturally, all forbidden sexual unions are naturally performed by consenting adults, each one making sure he or she is unobserved. Verse 20 speaking of someone sleeping with his father’s wife (former, not his mother) is also something which normally occurs in the male’s home, the place he grew up in, where he is not an intruder. Intercourse with animals clearly occurs in the privacy of the home or the animal’s pen, no one wanting to take a chance at being found out in such depraved behaviour. All other incestuous couplings are presumed to take place at home and with consent of the second party.

ארור אשר לא יקים, this is a blanket curse applying to all sins committed in private, the sinner making sure he is not observed.