The Solution for a cold heart. Jesus warned us in Matthew 24 that the “love of many will grow cold”
The answer for that is found in another end time scripture of I Cor 15. Paul says at the end of the chapter to be “steadfast, Immovable, always abounding in the work of the Lord – Knowing that it is NEVER in vain.
What we do for God counts when done for him and that gives us a complexly different perspective and help for a heart that faces disappointments and grows cold.