expression
wholeheartedly; with all one's heart
Expresses doing something with sincere feeling, care, or devotion. Often used as an adverbial phrase modifying a verb.
心を込めて手紙を書いた。
I wrote the letter with all my heart.
彼女は心を込めて歌を歌った。
She sang the song wholeheartedly.
A set phrase composed of 心 (heart, mind), the object marker を, the continuative form of 込める (to put into), and the conjunctive particle て. Literally 'putting one's heart into it'.