Is a prayer for the conversion of sinners to one of the kingdom of God ?

Yes, in Christian belief, praying for the conversion of sinners is an essential part of the life and mission of the Kingdom of God. 

This idea is rooted in several key theological concepts:

• Jesus' Call to Repentance: The proclamation of the Kingdom of God began with Jesus' call to "Repent and believe in the gospel, for the kingdom of God is at hand". Conversion (a change of heart and turning away from sin toward God) is the necessary response to this message.

• God's Desire for Salvation: Christian theology emphasizes that God "wills not the death of a sinner, but his conversion". Praying for this aligns the believer's heart with God's own merciful intentions for the world.

• Intercessory Prayer: Believers are commanded to "pray for one another". Praying for the salvation of others is a powerful form of intercession, recognized as a way to participate in God's redemptive work on Earth and help bring others into the Kingdom of Grace.

• Expansion of the Kingdom: The expansion of the Kingdom of God on Earth involves the spiritual growth of believers and the conversion of those who do not yet know Christ. Prayer is considered a primary spiritual weapon for breaking down spiritual strongholds and opening doors for the gospel to be received.

• Personal Transformation: While prayer for others impacts them, it also transforms the person praying, helping them align their will with God's will and develop virtues like compassion and love, which are characteristics of those living in the Kingdom of God. 

Therefore, praying for the conversion of sinners is a core aspect of living out one's faith and actively participating in the coming of God's Kingdom on Earth.