Big thanks to Tom Wood for highlighting these insightful words from Richard Lovelace:
Christians who are no longer sure that God loves and accepts them in Jesus, apart from their present spiritual achievements, are subconsciously insecure persons--much less secure than non-Christians--because they have too much light to rest easily under the constant bulletins they receive from their Christian environment about the holiness of God and the righteousness they are supposed to have. Their insecurity shows itself in pride, a fierce defensive assertion of their own righteousness and defensive criticism of others. They come naturally to hate other cultural styles and other races in order to bolster their own security and discharge their suppressed anger. They cling desperately to legal, Pharisaical righteousness. But envy, jealousy and other branches on the tree of sin grow out of their fundamental insecurity.
It is often necessary to convince sinners of the grace and love of God toward them, before we can get them to look at their problems. Then the vision of grace and the sense of God's forgiving acceptance may actually cure most of the problems.
This may account for Paul's frequent fusing of justification and sanctification.