tā / zài / xìn / zhōng / biǎo / dá / le / zhì / qiè / de / sī / niàn / zhī / qíng / ràng / mǔ / qīn / fēi / cháng / gǎn / dòng

他在信中表达了挚切的思念之情，让母亲非常感动。

He expressed his sincere longing in the letter, deeply touching his mother.