Extremely beautiful and profound questions.
1. Is God's grace hard to receive? The wind of Grace is always blowing, but it requires a receptive heart. Grace is like sunshine, if we keep our curtains open, then we will receive it. Equally, if we keep our curtains closed or shut, then it cannot come in.
2. What exactly is required for someone to receive Grace? Love of God, steadfast daily prayer and interior prayer, service and an exemplary life. St. Paul exhorts us to be imitators of Christ, and our Lord Himself asks us to 'seek and ye shall find' 'knock and the door shall be opened unto you.' In other words, yearning, longing or earnestness is necessary. We must want the life of the Divine. Here this would be accompanied by discipline, steadfastness, prudence, and one-pointed devotion to this Cause. We cannot serve two Masters. It is either God, or the slavery and attachment to worldly and material desires.
Here I speak of attachment or slavery. I wish to make it quite clear that seeking things to utilise here on earth for heavens sake, I perceive differently from seeking things for their own sake. Finally, the descent of Grace requires purity of heart, a clear conscience and a life of gratitude to the Supreme. The Christ tells us that it is the things inside that can defile us: doubt, greed, lust, insecurity, jealously, anger, greed and many others. They consequently minimise or block the descent of grace.
3. What spiritual value does God's grace have on someone's life? Grace is imperative. The strength we require to serve others or love others indeed our Lord Himself, comes from the descent of the Holy Spirit, from Grace. It is this which transforms our inner nature and burns away our ignorance. We cannot do this alone. Prayer is essential, as well as humility before God, the ability to bend like a yielding tree.
4. Can someone who has God's grace lose it because of sin after they accept God's grace? Yes. We can forget God or become diverted through modern 'clusters' in our lives and 'consumerism', etc. Still, Grace is not truly lost and will remain until we are again ready to approach the Divine.
5. Has everybody been offered grace or just the select few? The good mother sends all her children to school. Some may do well and others not so well for different reasons. This kind of story is reflected in the parable of the sower. Grace is there for all, but some, by virtue of their childlike nature, their seeking, are more receptive than others.