For as many as are led by the Spirit of God, they are the sons of God.
Romans 8:14 KJV
The evidence of being a son is following the lead of the Spirit.
But if ye be led of the Spirit, ye are not under the law.
Galatians 5:18 KJV
And if we are sons, then we are no longer under the law.
For the flesh lusteth against the Spirit, and the Spirit against the flesh: and these are contrary the one to the other: so that ye cannot do the things that ye would.
Galatians 5:17 KJV
Our flesh and Spirit are at odds with one another. To seek to please the flesh is the opposite of being led by the Spirit.
When you follow the desires of your sinful nature, the results are very clear: sexual immorality, impurity, lustful pleasures, idolatry, sorcery, hostility, quarreling, jealousy, outbursts of anger, selfish ambition, dissension, division, envy, drunkenness, wild parties, and other sins like these. Let me tell you again, as I have before, that anyone living that sort of life will not inherit the Kingdom of God.
Galatians 5:19-21 NLT
These are characteristics of seeking after our fleshly desires. To do so does not negate our sonship, it reveals that we aren’t sons at all.
For ye have not received the spirit of bondage again to fear; but ye have received the Spirit of adoption, whereby we cry, Abba, Father. The Spirit itself beareth witness with our spirit, that we are the children of God:
Romans 8:15-16 KJV
The longing of a sons heart is to please his Father. Gods Spirit confirms with our spirit by making the cry of our heart cry out, Daddy, Papa, Father. He confirms us as sons by making our hearts greatest desire a closeness with Him.