Along with the previous verse from John, I think this is the main verses the OSAS base their doctrine on.
Romans 8:35 Who then shall separate us from the love of Christ? Shall tribulation? Or distress? Or famine? Or nakedness? Or danger? Or persecution? Or the sword? 36 (As it is written: For thy sake, we are put to death all the day long. We are accounted as sheep for the slaughter.) 37 But in all these things we overcome, because of him that hath loved us. 38 For I am sure that neither death, nor life, nor angels, nor principalities, nor powers, nor things present, nor things to come, nor might, 39 Nor height, nor depth, nor any other creature, shall be able to separate us from the love of God which is in Christ Jesus our Lord.
Here are a few others I think are related.
2 Corinthians 1:21 And it is God who establishes us with you in Christ, and has anointed us, 22 and who has also put his seal on us and given us his Spirit in our hearts as a guarantee.
2 Corinthians 5:5 He who has prepared us for this very thing is God, who has given us the Spirit as a guarantee.
Ephesians 1:13 In him you also, when you heard the word of truth, the gospel of your salvation, and believed in him, were sealed with the promised Holy Spirit, 14 who is the guarantee of our inheritance until we acquire possession of it, to the praise of his glory.
So I think the main concept is that none of our actions can save us, so none of our actions condemn us. I don’t think it’s viewed as a license to sin, but a rejection of the need for last rites and final confession so one dies in a state of grace.