What does the Bible mean by 'creating a clean heart'?

The plea to 'create in me a clean heart, O God' (Psalm 51:10) signifies the need for divine renewal and transformation. This reflects a deep yearning for spiritual rebirth, wherein God intervenes and gives a new nature. In Reformed theology, this corresponds to the doctrine of regeneration — the act where the Holy Spirit brings life to a believer’s soul, ensuring that they are not simply reformed on the outside, but fundamentally changed on the inside. It implies that believers cannot achieve such a transformation on their own; they can only receive it as a gift of grace from God.