When you feel like it’s just not worth trying to preach the gospel anymore – when you feel like giving up – and you’re discouraged – when you feel you’re getting nowhere – that what you do seems to amount to nothing………
Then ask yourself, Why do I do anything at all? Ask yourself, Self, what motivates you? Why do you do anything? What’s in it for you?? Self, give me a reason!
It’s gotta be love.
Love keeps us going when we come to the end of everything else.
For the love of Christ CONSTRAINS [Sunecho] us... 2 Corinthians 5:14
This means the love of Christ has arrested us! His love has taken hold of us in a way that we are compelled to preach the gospel, we cannot keep silent. His love won’t allow us to be silent.
Like, you were seeing people about to walk over a cliff and you felt CONSTRAINED to say something. The love of Christ for these people constrained you to speak to them. If you didn’t have the love of Christ then you wouldn’t care enough to warn them.
Ian Vincent 
December 13, 2011 at 2:15 am
The constraining power or constraint of the love of God works both, in compassion for the lost, and also a strong desire that they know the love of God.
Love that wants to see them saved, and also that desires that they know this love for themselves.
A strong desire they be saved AND that they come to KNOW the Savior who loves them!
Overarching the whole thing is our personal love for God. Even if i found that i couldn’t love a certain person, or couldn’t feel any love for them, i would decide to love them anyway, just bcos of the fact that God loves them.