For ye are all the children of God by faith in Christ Jesus. – Galatians 3:26

Faith is the mark of sonship in all who have it, whoever they may be, for ye are all the children of God by faith in Christ Jesus. If you are believing in Jesus, whether you are Jew or Gentile, bond or free, you are a son of God. If you have only believed in Christ of late and have but for the past few weeks been able to rest in His great salvation, yet, beloved, now are you a child of God. It is not an after privilege, granted to assurance or growth in grace; it is an early blessing, and belongs to him who has the smallest degree of faith, and is no more than a babe in grace. If a man be a believer in Jesus Christ his name is in the register-book of the great family above, “for ye are all the children of God by faith in Christ Jesus.” But if you have no faith, no matter what zeal, no matter what works, no matter what knowledge, no matter what pretensions to holiness you may possess, you are nothing, and your religion is vain. Without faith in Christ you are as sounding brass and a tinkling cymbal, for without faith it is impossible to please God. Faith then, wherever it is found, is the infallible token of a child of God, and its absence is fatal to the claim.

Henceforth you are one in Christ, you wear his name, you live in him, you are saved by him, you are altogether his. Now, if you are one with Christ, since he is a son, you are sons also. If you have put on Christ God seeth you not in yourself but in Christ, and that which belongeth unto Christ belongeth also unto you, for if you be Christ’s then are you Abraham’s seed and heirs according to the promise. ~ C.H. Spurgeon

https://www.blueletterbible.org/Comm/spurgeon_charles/sermons/1435.cfm