정성 = a sincere desire to help, contribute, give care. 모으다 = to gather/accumulate to make something plentifil or greater. So 정성을 모으다 = bring one's good will together = be like a praying angel to someone / for a good cause. 정성을 모아 도와드리겠습니다 = We'll do everything we can to help you. 정성을 모아 마련한 선물 = a gift that is the product of reaching out hearts. 정성 is one of those very nice words meaning sincere and true intentions - an opposite of cursory, gesture only, etc.