Q. Why do we make a fuss of the first of a month when there is a much more impressive moon in the middle of the month?
For some purposes, however, we also need to take account of the solar months.
Pesach, for instance, has to be a spring festival, and if we adhered strictly to the lunar months we would lose roughly 11 days a year and it would end up in the wrong season. Therefore we adjust the lunar calendar to the solar by adding an extra (“leap”) month seven times in 19 years.
There are many explanations of why we attach significance to the beginning of the month. The phases of the moon symbolise how man’s perception of God waxes and wanes; when the moon is small we have a keen sense of aspiration to encounter God, and when it is full we rejoice at a moment of spiritual fulfilment.
The moon’s phases also represent the Jewish experience, alternating between times of hope, times of fulfilment and times of growing darkness.