"The condition acceptable to God" means being pleasing to God. Why would being pleasing to God cause one to "be filled?"
The word "be filled" is being translated from the Greek word χορτάζω (chortazō) which means "to fill or satisfy" according to the lexicon. Each of us is looking for fulfillment and satisfaction. We seek fulfillment as we seek sexual pleasure, fame, wealth, family, relationships with others, the approval of others and so on.
In fact, each of us is seeking fulfillment. But we are seeking fulfillment in the wrong place.
It might be compared to a driver who is hungry taking his car to the gas station and filling his car up with gas and thinking that when the car is full of gas he will no longer feel hungry.
Why isn't the driver full when the gas tank is full?
Because the driver is not the car.
In the same way, we are not these physical bodies. These physical bodies are like vehicles, and we are the driver of this vehicle, the physical body.
This is proven by hundreds of thousands of clinical death cases where a person rises above their body and looks at it from above. In clinical death, the person separates from the physical body because the person is not the physical body.
We are spiritual in nature, not physical. Our bodies are temporary - they will each die in a few decades. But we - the spirit-person within - will live on after the body dies.
Where does the spirit-person within come from? The spiritual dimension.
For this reason, the physical things of this world do not satisfy us. Just as Jesus is teaching, we need spiritual "food" to fulfill us.
And what is that 'spiritual food'? It is a loving relationship with the Supreme Being.
No matter our predicament in life, each of us is seeking love. We seek love as we try to impress others. We seek love as we go on dates. We seek love as we marry. We seek love as we have a family. We seek love as we want our kids or our spouse or our family to care about us. We seek the approval of others because we need others to love us and care for us.
And we need to love and care for others in return.
This is why we work so hard for our family, or spouse, or to impress others, or to achieve fame. We need love. It is the fuel that we burn. It is the stuff that feeds us.
But the various "loves" of this physical world are only temporary. They come and go, and they are typically conditional: They are contingent upon what we can give the other person. When they no longer need us, their so-called love typically goes away. Or their body dies and they leave us.
But the love of the Supreme Being is unconditional. He loves us whether we love Him or not. He loves us and cares for us whether we care about Him or not.
This is because the loving relationship between ourselves and the Supreme Being is the love that we are always seeking. It is the perfect, unconditional love we are always pining for.
And just as pleasing the one we love is important to any loving relationship, this is the stuff of the loving relationship that exists between each of us and the Supreme Being.
Just consider what we do when we want to please the one we love: We bring them a flower, or we do something for them. What is this? It is loving service, and certainly our beloved is pleased with such loving service.
When this love and loving service is pointed towards the Supreme Being - it fulfills our spirit-person. This is spiritual life, and this is the only thing that can completely fulfill our need for love - pleasing the Supreme Being - as Jesus stated - "for they will be filled."
This understanding is confirmed by Jesus' most important instruction:
“‘Love the Lord your God with all your heart and with all your soul and with all your mind.' This is the first and greatest commandment." (Matt. 22:37-38)
(For a translation of Jesus' statements from the Gospel of Matthew without institutional sectarian influence, see the Devotional Translation - translated from the original Greek texts.)