Why does God call sinners to become His instruments of Glory?

God calls sinner to repentance first before anything else.

Luke 3:8-9 (KJV)

Bring forth therefore fruits worthy of repentance, and begin not to say within yourselves, We have Abraham to our father: for I say unto you, That God is able of these stones to raise up children unto Abraham.
And now also the axe is laid unto the root of the trees: every tree therefore which bringeth not forth good fruit is hewn down, and cast into the fire.

It's only after they repent that they can start talking of glory.

If they don't repent, no glory but hell fire awaits.

God bless.

Where did Jesus call sinners to be instrument of his glory?

The call and the gift of God is without repentance.