'Nor let us make trial of the Lord, as some of them made trial, and perished ('were perishing') by the snakes.'
Again they tested the Lord by looking back and comparing their present state with the past (Numbers 21:4-9 compare Psalms 78:18), an ever present danger in times of trial. The result for them was God's judgment in the form of the poisonous snakes in the camp. Their past spiritual experiences did not save them. So neither Paul nor the Corinthians must put themselves in danger of looking back (compare 1 Corinthians 9:26). It could be even worse for them.
Note: Some MS have 'the Lord'. Some have 'Christ'. Some have 'God'. 'The Lord' is found for example in Aleph and B. P46, D, G have 'Christ', easily seen as interpretive of 'the Lord'. A has 'God', again interpretive. An original 'the Lord' easily explains both variances, the change being made for clarity. But the matter is not certain.