Hi Bonsoir:
I found this list www.highfrequencywords.org/hfw100fp.pdf, which is more or less the same as the one my DDs received in KS1 - you haven't said, but I'm presuming it's for KS1.
Why are you getting these? Odds are your DC was tested in class and they are selecting those words that are a difficulty. The high frequency words are random I'm afraid. If you look at them there may be little rhyme or reason in learning to spell these first but most are straightforward phonetically and although there are a few which are much more complex (Mr, Mrs, off, people). The point is that these are words that children will most typically also learn to read first, because they are so frequently present in children's stories for 4 - 6 year old reading age.
I realise the spelling would make more sense if it were working on phonemes (-at words - hat, cat, bat, sat, or -long o sounds - home, foam, roam, etc...) but it may be that the teacher wants to start here first and then move on to more complex phonemes (words ending in -al or words using -igh or -ough).
We had these 100 high frequency words as spelling words as well and we also found it difficult to explain why it's 'of' and 'off' but just played silly memory games. I used to make up stories to remind my DDs about the spelling: Mum told the two naughty 'fs' to stop jumping up and down and get off the sofa. I know their, they're and there nearly killed us. (Our trick was there is a 'here' in 'there', he and i bought a house and now people say that's their house. So remember 'their' has he and i. and they're is squishing they and are together and the poor 'a' just popped right out. Mad and desperate but it worked).
We actually had more success pointing out the spelling words in reading books than we did having our DDs write them out or practice spelling them out loud. I think it helps to take the long view on this - eventually they will have to learn it - so better sooner than later.
Hope that helps - and good luck.