1 Chronicles 28:9

9 `And thou, Solomon, my son, know the God of thy father, and serve Him with a perfect heart, and with a willing mind, for all hearts is Jehovah seeking, and every imagination of the thoughts He is understanding; if thou dost seek Him, He is found of thee, and if thou dost forsake Him, He casteth thee off for ever.

1 Chronicles 28:9 Meaning and Commentary

1 Chronicles 28:9

And thou, Solomon my son
Who was present in this assembly, and presented to them by David as his successor, and their future king: and having addressed them, he turns himself to him, and exhorts him, saying,

know thou the God of thy father;
who was his Father and covenant God, and whom he served and worshipped, and who had bestowed upon him many favours, both temporal and spiritual; and having had such an experience of his goodness, he exhorts his son to seek to know more and more of him, and to own and acknowledge him as his God, and to love and fear him:

serve him with a perfect heart, and with a willing mind;
cordially and sincerely, cheerfully and freely, neither in an hypocritical manner, nor through force and constraint, nor with loathing and weariness:

for the Lord searcheth all hearts;
the hearts of all men, even of kings, and knows from what principles and with what views and in what manor they serve him:

and understandeth all the imaginations of the thought;
not only the thoughts of the heart, when regularly formed and ranged in order, hut even the very beginning of them, the first motions of the mind, and before they are well formed, see ( Genesis 6:5 ) ( Psalms 139:2 )

if thou seek him;
by prayer and supplication in his house and ordinances:

he will be found of thee;
grant his presence and bestow his favours, see ( Isaiah 4:6 )

but if thou forsake him:
his word, his ways, his worship:

he will cast thee off for ever;
from being king, or enjoying that peace, prosperity, and happiness, which otherwise would be enjoyed.

1 Chronicles 28:9 In-Context

7 and I have established his kingdom to the age, if he is strong to do My commands, and My judgments, as at this day.
8 `And now, before the eyes of all Israel, the assembly of Jehovah, and in the ears of our God, keep and seek all the commands of Jehovah your God, so that ye possess this good land, and have caused your sons to inherit after you unto the age.
9 `And thou, Solomon, my son, know the God of thy father, and serve Him with a perfect heart, and with a willing mind, for all hearts is Jehovah seeking, and every imagination of the thoughts He is understanding; if thou dost seek Him, He is found of thee, and if thou dost forsake Him, He casteth thee off for ever.
10 See, now, for Jehovah hath fixed on thee to build a house for a sanctuary; be strong, and do.'
11 And David giveth to Solomon his son the pattern of the porch, and of its houses, and of its treasures, and of its upper chambers, and of its innermost chambers, and of the house of the atonement;
Young's Literal Translation is in the public domain.