Christ’s sacrifice is an event which is still celebrated in the New Testament version of Passover: the Lord’s Supper (Matthew 26:17–29). This is clearly the festival
that Paul is referring to. Possibly, the New Testament church retained the use of unleavened bread for their celebrations of the Supper. This would lend special poignancy to Paul’s words in this verse.
Unrepentant sinners should not be allowed to take part in the Lord’s Supper (see also 1 Corinthians 11:27–31). Paul’s warning goes further than only the specific case of immorality discussed in verses 1 Corinthians 5:1–5. He admonishes the Corinthians to purify themselves from all forms of malice and evil.
The contrast between old dough and unleavened dough corresponds to the contrast which Paul draws elsewhere between the old man
and the new man
(Ephesians 4:22–24; Colossians 3:9–10).
8 Célébrons donc la fête, non avec du vieux levain, non avec un levain de malice et de méchanceté, mais avec les pains sans levain de la pureté et de la vérité.