Thankfulness is of various kinds. There is a verbal thanksgiving which is confined to a mere utterance of gratitude. This is of no importance because perchance the tongue may give thanks while the heart is unaware of it.
One may say thank you a thousand times while the heart remains thankless, ungrateful.
Consider how grateful anyone becomes when healed from sickness, when treated kindly by another or when a service is rendered by another, even though it may be of the least consequence. If we forget such favors, it is an evidence of ingratitude. Then it will be said a loving-kindness has been done, but we are thankless, not appreciating this love and favor.
Physically and spiritually we are submerged in the sea of God's favor. He has provided our foods, drink and other requirements; His favors encompass us from all directions. The sustenances provided for man are blessings. Sight, hearing and all his faculties are wonderful gifts. These blessings are innumerable; no matter how many are mentioned, they are still endless.
Spiritual blessings are likewise endless -- spirit, consciousness, thought, memory, perception, ideation and other endowments.