Serving God is meant to be an avenue for accessing God’s rewards.
But services are rewardable only when they are acceptable and doing it right is what makes it acceptable.
It is unacceptable when it is done deceitfully.
Rendering service negligently and with slackness attracts curses. Jer.48:10
To escape deceitful service, serve heartily i.e excitedly and cheerfully, as to the lord. Col.3:23-25