The normal understanding in Christianity is that sin brings separation from God. However is there biblical basis for holding to the belief that separation from God is in itself sin rather than a consequence of sin?
I can think of one clear-cut verse off the top of my head. Assuming that the question you are asking is about one who was once not separated from God but later became separated (actually this is true for all man if you think about it, since man was with God at the beginning and later separated himself from God)
Of course, you can also read into the context of the Bible and see. When man decided to eat of the tree of knowledge of good and evil rather than the tree of life, he actively made a choice to choose the representative of Satan (tree of knowledge) over God (the tree of life). In this way, the original sin itself is actually the act of separating himself from God in the way of disobedience.
Your question is very direct and simple yet it is profound in its implications. Sin is a relational breach from God and the remedy for sin is a restored relationship with God. This we emphatically have with Jesus Christ.
If we look at the relational claims of Christ:
The relational commandment upon which all the law rests:
The eternal security of our relationship with God:
How we will abide:
The eating of the Tree of knowledge of “good and evil” isolated man from the will of God the Father. Jesus Christ is at the mercy of the will of God the Father thus works which originate from our own sovereign wills will consistently fall short of the mark.
The sealing presence of the Holy Spirit makes manifest the will of the Father in our lives: