It is equally true that adoption lays on one the abiding obligation to keep the law, as the means of pleasing one's newfound Father. Adoption puts law-keeping on a new footing: as children of God, we acknowledge the law's authority as a rule for our lives, because we know that this is what our Father wants. The sins of God's children do not destroy their justification or nullify their adoption, but they mar the children's fellowship with their father. 

packer, knowing god, pg 223

The establishing of the child's status as a member of the family is only a beginning. The real task remains: to establish a genuinely filial relationship between your adopted child and yourself. It is this, above all, that you want to see. Accordingly, you set yourself to win the child's love by loving the child. You seek to excite affection by showing affection. So with God. And throughout our life in this world, and to all eternity beyond, he will constantly be showing us, in one way or another, more and more of his love, and thereby increasing our love to him continually. The prospect before the adopted children of God is an eternity of love.

Knowing God, Packer, pg 216

But things are not like that in God's family. there you have absolute stability and security; the parent is entirely wise and good, and the child's position is permanently assured. The very concept of adoption is itself a proof and guarantee of the preservation of the saints, for only bad fathers throw their children out of the family, even under provocation; and God is not a bad father, but a good one. When one sees depression, randomness, and immaturity in Christians one cannot but wonder whether they have learned the health-giving habit of dwelling on the abiding security of true children of God.

Gal 4:7 So you are no longer a slave, but a son; and since you are a son, God has made you also an heir

1 Jn 3: 1 How great is the love the Father has lavished on us, that we should be called children of god!

Rm 8:15 For you did not receive a spirit that makes you a slave again to fear, but you received the Spirit of sonship. And by him we cry, "Abba, Father."

Eph 1:5 He predestined us to be adopted as his sons through Jesus Christ, in accordance with his pleasure and will

All those that are justified, God vouchsafeth, in and for His only Son Jesus Christ, to make partakers of the grace of adoption: by which they are taken into the number, and enjoy the liberties and privileges of the children of God; have His name put upon them, receive the Spirit of adoption; have access to the throne of grace with boldness; are enabled to cy, abba, Father; are pitied, protected, provided for, and chastened by Him, as by a father; yet never cast off, but sealed to the day of redemption, and inherit the promises, as heirs of everlasting salvation.

Westminster Confession, Chapter 12

You sum up the whole of New Testament teaching in a single phrase, if you speak of it as a revelation of the Fatherhood of the holy Creator. In the same way, you sum up the whole of new Testament religion if you describe it as the knowledge of god as one's holy Father. if you wnat to judge how well a person understands Christianity, find out how much he makes of the thought of being God's child, and having God as his Father. if this is not the tought that prompts and controls his worskhp and prayers, and his whole outlook on life, it means that he does not understand Christianity very well at all. for everything that Christ taught, everything that makes the New testament new, and better than the Old, everything that is distinctively christian as opposed to mrely Jewish, is ummed up in the knowledge of the Fatherhood of God. "Father" is the Christian name for God.

Packer, Evangelical Magainze 7, pp 19 -20.