My reply didn't argue that sin is harmless or that believers should continue in it. The issue here is the timing & scope of Christ's forgiveness upon the Holy Spirit's sealing.
The Titus 3 & Ephesians 1:13-14 posted explicitly place at the moment a person believes the gospel—before any works, rituals, or performances. That sealing is God's guarantee that all sins-past, present & future-have been forgiven through faith placed in Christ's sin atoning death & resurrection. Jesus payment was a once-for-all-sin sacrifice.
Vine’s Expository Dictionary definition posted reinforces this by distinguishing present salvation (justification, regeneration, sealing) from the future deliverance of believers at Christ's return, a deliverance Scripture says is assured to those already justified.
Of course sin has consequence & the consequence from sinning could manifest itself, in many different ways. A health issue, a broken relationship, disease, lost rewards earned etc. That being said the believers salvation is secure, simply stated, eternal life is ETRENAL!