God owes us nothing
Williams Perkins reminds us that even Adam could not merit eternal life
William Perkins:
What can we any way deserve, when our full recompense must be of mercy? And this appears further by Adam: If he had stood to this day, he could not by his continual and perfect obedience have procured a further increase of favor at God's hand but should only have continued [in] that happy estate in which he was first created.1
According to Perkins, Adam was never promised that he must merit eternal life, so that God would be in debt to Adam, or that Adam on his own standing could “sue” God for that debt (cf. Rom. 4:4). However, God did provide by covenant that he would reward Adam if he met a certain condition, namely, obedience.
As the Westminster Confession of Faith teaches (at ch. VII.i), we reasonable creatures owe God our obedience, but we could never have any blessing from him unless God voluntarily condescended to us by way of covenant. This is not a consequence of the fall, but rather a (necessary) feature of creation.
The point is that we creatures owe our Creator everything, and he owes us nothing. Everything God gives us, or could ever give us, is a gift.
1 William Perkins, A Reformed Catholic (Moscow, ID: Canon Press), 67-68
