One drop of human merit in a sea of free grace?

The following is from Spurgeon's sermon,
"Robbers of God" No. 2156. Malachi 3:8.

Many rob God by rebelling against his sovereignty.

I have known men bite their lip and grind their teeth in
rage whom I have been preaching the sovereignty of God.

"Therefore God has mercy on whom he wants to have mercy,
and he hardens whom he wants to harden." Romans 9:18

Men seem to think that God is under obligation to
grant salvation to guilty men; that if he saves one
he must save all.

They talk about rights, as if any man had any right
before the throne of God, except the right to be
punished for his sin.

Mercy can only be shown to the guilty on the
ground of the royal prerogative. It must be the
free act of God's grace, done at his own good
pleasure if any guilty man be saved from death.

The doctrinaires of today will allow a God, but he must
not be King: that is to say, they choose a god who is
no god, and rather the servant than the ruler of men.

We, however, declare on God's behalf, that
"It does not, therefore, depend on man's desire
or effort, but on God's mercy." -and at the sound
of this doctrine they stamp their foot with rage.
They would rob God of his crown, and leave him
neither throne, nor will.

This will not do for me; my heart delights to say,
"It is the Lord: let him do what seems good to him."
Whatsoever is his pleasure shall by my pleasure.

Even if the Lord condemn me, I cannot say that he
is unjust. But if he has mercy upon me, I must
ascribe it wholly to his free and sovereign grace.

Do not rob God of his sovereignty; but rejoice
that the Lord reigns and does as he wills.

God's free grace is one of the brightest jewels of his crown!

God saves not according to merit, but according to mercy!

"The wages of sin is death; but the gift of God is eternal life."
Salvation is freely given, not because man merits it, but
because Jehovah wills it.

All salvation is of grace, and not of works.

I say it is of free grace- Salvation comes because God
wills to save. Grace is given to the most unworthy of the
sons of men, to show that it is of grace, and not of debt.

One drop of human merit put into
a sea of free grace
will spoil it all.

"And if by grace, then it is no longer by works; if it
were, grace would no longer be grace." Romans 11:6