Here are two lines of the lyrics in a specific song:

[出]{で}[逢]{あ}いしは [運命]{さだめ}か


[纏]{まと}いしは [緋]{ひ}[色]{いろ}の[棘]{とげ}の[鎧]{よろい}

I'm 99% sure that the し here is the 連体形 of き; it follows the 連用形 of [出]{で}[逢]{あ}う and [纏]{まと}う.

However, what I don't understand is why the 連体形 is being used and what it means for は to directly follow the 連体形 of a (auxiliary) verb. It would still make sense if the し was removed from both lines - is the し only there for emphasis on the fact that it happened in the past, or does it have some sort of other nuance or meaning or grammatical construction that I don't know of?

Thanks in advance!