The right attitude of the Christian should never be “God shows me grace, so I can keep sinning!” Instead, the right attitude that we see here is “God shows me grace, so I can keep obeying!”
By teaching us this prayer, Jesus is summoning us into the presence of Our Father, day after day, not to hear His voice accusing us, but to hear his voice acquitting us.
When we trust in our great King – when we believe in Jesus – he saves us, not because of any virtue or strength in us, but because of the virtue and strength that’s in him.