This is the law that should govern our whole life. We are meant for loving which is a matter of serving others. If that loving is authentic, inspired by God's love, then it is shown in serving others wholeheartedly without counting the cost or expecting any return. It's completely done for free.
This truth about ourselves is amply dramatized in that lesson Christ gave regarding the unprofitable servant. (cfr Lk 17,7-10) "When you have done all you have been commanded," Christ said, "say, 'We are unprofitable servants. We have done what we were obliged to do.'"
Loving and serving cannot and should not be quantified in terms of cost and reward. It is above all these considerations. It's a purely spiritual operation that should not be spoiled by giving it some material and temporal value. It's where we can approximate, keep and build up that dignity of being the image and likeness of God and adopted children of his, how we become God-like.
As man, we have our material and temporal needs. These should be attended to also. We are body and soul, material and spiritual, and both dimensions have their distinctive requirements that have to be met.
In our earthly life, these two dimensions and components of our being are inseparable. Just the same, we should not confuse them. We have to abidingly acknowledge their difference and learn how to handle this condition properly.
Of these two components, the spiritual aspect has pride of place, since as Christ said: "It is the Spirit that gives life. The flesh counts for nothing." (Jn 6,63) In other words, our material and temporal dimension would have no value unless properly inspired by the Spirit who together with giving us life also inspires us to love, to give ourselves freely to others.
Remember what St. Paul said: "If I give all I possess to the poor and give over my body to hardship that I may boast, but do not have love, I gain nothing." (1 Cor 13,3) Christ himself said: "What does it profit a man if he gains the whole world but loses his own soul?" (Mk 8,36)
It's this Spirit-inspired loving that makes serving and self-giving an affair where we gain and receive more the more we give ourselves to others. These are what Christ said in this regard:
"Give, and it will be given to you. A good measure, pressed down, shaken together and running over, will be poured into your lap. For with the measure you use, it will be measured to you." (Lk 6,38) And, "Freely you have received, freely give." (Mt 10,8)
This is how God serves and gives himself to us, with complete gratuitousness. He even goes all the way of still loving and serving us even if we do not reciprocate his love properly. This is how we should serve and give ourselves to the others also.
This will require a deep sense of humility and detachment from earthly things, which does not mean that we have no need for them. Our need for them will be fully satisfied if we give ourselves first to God, for as Christ said:
"Seek first the kingdom of God and his righteousness, and all these things shall be added unto you." (Mt 6,33)