Isaiah 55:6,7

Seek the LORD while He may be found; 

Call upon Him while He is near. 

Let the wicked forsake his way 

And the unrighteous man his thoughts; 

And let him return to the LORD, 

And He will have compassion on him, 

And to our God, 

For He will abundantly pardon.

True seeking in faith is accompanied by repentance, which is described as forsaking ways and thoughts and turning from sinful living to the Lord.  A sinner must come believing in God, recognizing his sin and desiring forgiveness and deliverance from that sin.  At the same time he must recognize his own inability to be righteous or to satisfy God and cast himself on God's mercy. It is then that he receives complete pardon.  His sin has been covered by the substitution of the Messiah in his place.  

John MacArthur