If you fast and avoid a mode of life which excites the passions, and in general do whatever contributes to your deliverance from evil, then you have ‘prepared the way for the Lord’.
But if you do these things out of selfesteem, or greed, or love of flattery, or for some similar motive, and not with a desire to perform God’s will, then you have not ‘made His paths straight’.
You have endured the labor of preparing the way but do not have God walking in your paths.
St Maximos the Confessor
The Philokalia – Vol II