We ought to walk in awareness of the HolySpirit in us such that all our thoughts are shared with Him and processed in accordance with His Word.
In so doing, we pray without ceasing.

Prayer is communication with the HolySpirit. Since we are in partnership with the HolySpirit keeping the lines of communication open is critical for the successful operation of the partnership.

Think of how a singing duet must be aware of what each other is doing in order for them to hit the right note and the right syllable at the same time to produce harmony.

Praying is harmonizing with the HolySpirit.