A sinning saint is of no earthly use like a bird without wings is of no flying good. What we mean by this is that a sinning Christian remains as a light hidden underneath a bushel, and as a tasteless salt.
Ask any converted Christian who willingly indulge in sin about their productivity or communion with God and general happiness. I am sure the majority will say, 'O ken, they played the flute and I could not dance. And whenever I do it is always with a forced smile.'
A sinning saint therefore is a miserable Christian in his heart because surely the Spirit cannot be happy with such a child who has become a rebel. The Spirit being who he is must be grieved by such a one for he cannot rejoice on his behalf. But the quick tongue Christian might say, 'but ken are we not all sinners? And is it not true that in this life we shall never cease from sinning. Because if it is not this sin then it is that sin.'
O child, tell me this. Has Christ the power to save us from sin in this age? For you see, the individuals I am talking about are those who willingly, after being instructed about their wrongs by the Spirit or anyone else that knows God, continue in their sins, never ever coming to repentance. And I am also speaking of those who are currently hopeless about their sinning state. Although they feel the depths of their awful deeds, yet deep down, right down in their guts, they unnaturally enjoy that which they should hate, and feel as if they shall never forsake it, as to let it go as the frigtening girl her teddy bear.
As long as this is their condition, then truly they are of no earthly use. I do not mean to say this harshly but to serve as an awakening unto self-reflection. A sinning Christian is of no earthly use, as a dead female dog to her puppies.
Of course God can use our sins to accomplish his own ends, which glorifies him as he did with the sins of those terrible soldiers that nailed his Son to that cursed tree. He used their wickedness to grant his people redemption and salvation. Likewise, a struggle with a particular sin may be God's instrument to do something in your life although he wishes you to forsake it and cling unto him instead.
God can use our sins for his glory, and when by grace the sinning saint comes back to his senses and kisses holiness by embracing the gospel and the forgiveness and righteousness that comes through it, the Christian will now consider grace all the more sweeter and love God all the more as well.
But these are only my musings, the words of a fallible boy. I may be wrong as the fool who says that there is no God, but Christ is always right especially when he says, 'You are the salt of the earth, but if salt has lost its taste, how shall its saltiness be restored? It is no longer good for anything except to be thrown out and trampled underfoot.'
But there is hope for you in God who can turn your ashes into gold. Cling unto him. Forsake sin and be useful about in the world. Christ can make you salty again. O yes he can.