Romans 6:1-10: "1 What shall we say then? Are we to continue in sin that grace may abound? 2 By no means! How can we who died to sin still live in it? 3 Do you not know that all of us who have been baptized into Christ Jesus were baptized into his death? 4 We were buried therefore with him by baptism into death, in order that, just as Christ was raised from the dead by the glory of the Father, we too might walk in newness of life.
"5 For if we have been united with him in a death like his, we shall certainly be united with him in a resurrection like his. 6 We know that our old self was crucified with him in order that the body of sin might be brought to nothing, so that we would no longer be enslaved to sin. 7 For one who has died has been set free from sin. 8 Now if we have died with Christ, we believe that we will also live with him. 9 We know that Christ, being raised from the dead, will never die again; death no longer has dominion over him. 10 For the death he died he died to sin, once for all, but the life he lives he lives to God."
1 Peter 3:18-22: "18 For Christ also suffered once for sins, the righteous for the unrighteous, that he might bring us to God, being put to death in the flesh but made alive in the spirit, 19 in which he went and proclaimed to the spirits in prison, 20 because they formerly did not obey, when God's patience waited in the days of Noah, while the ark was being prepared, in which a few, that is, eight persons, were brought safely through water. 21 Baptism, which corresponds to this, now saves you, not as a removal of dirt from the body but as an appeal to God for a good conscience, through the resurrection of Jesus Christ, 22 who has gone into heaven and is at the right hand of God, with angels, authorities, and powers having been subjected to him."
Titus 3:4-7: "4 But when the goodness and loving kindness of God our Savior appeared, 5 he saved us, not because of works done by us in righteousness, but according to his own mercy, by the washing of regeneration and renewal of the Holy Spirit, 6 whom he poured out on us richly through Jesus Christ our Savior, 7 so that being justified by his grace we might become heirs according to the hope of eternal life."
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These three texts are similar enough that it's difficult to say where or if the hymn draws from one more than the others. The first and last lines, however, ("God's own child, I gladly say it" and "I'm a child of paradise!") seem to refer to "becom[ing] heirs" in Titus 3:7.
The beginning of the fifth verse ("There is nothing worth comparing / To this life-long comfort sure!") seems to borrow from Romans 8:18: "For I consider that the sufferings of this present time are not worth comparing with the glory that is to be revealed to us."
