Spiritual warfare: the heart is a battle ground
Compare these two verses:
Proverbs 3:5-6 "Trust in the LORD with all thine heart; and lean not unto thine own understanding. In all thy ways acknowledge him, and he shall direct thy paths."
Romans 10:10 "For with the heart man believeth unto righteousness; and with the mouth confession is made unto salvation."
Therefore to believe unto righteousness is to trust in the LORD. It is with the heart that one believeth unto righteousness, and it is also by the heart that one should understand and be converted.
Matthew 13:15 "For this people's heart is waxed gross, and their ears are dull of hearing, and their eyes they have closed; lest at any time they should see with their eyes, and hear with their ears, and should understand with their heart, and should be converted, and I should heal them."
To trust in the LORD is not to lean unto our own understanding. Therefore the heart is a battle ground between trusting in the LORD and leaning unto our own understanding.
1 Corinthians 2:14 "But the natural man receiveth not the things of the Spirit of God: for they are foolishness unto him: neither can he know them, because they are spiritually discerned."
The natural man leans unto his own understanding but the spiritual man trusts in the LORD. There is a conflict between the two.
Romans 7:25 "I thank God through Jesus Christ our Lord. So then with the mind I myself serve the law of God; but with the flesh the law of sin."
In the earthen vessel of a born again believer is a new man created after the image of the LORD Jesus Christ. With the mind of the new man we serve the law of God ("we have the mind of Christ" 1 Corinthians 2:16) but with the flesh we serve the law of sin.
1 Corinthians 15:57 "But thanks be to God, which giveth us the victory through our Lord Jesus Christ."
The heart is a battleground but thanks be to God which giveth us the victory through our Lord Jesus Christ. That's why in Proverbs 3:6 we acknowledge him. God is the one who direct the paths of his children through the words of the LORD (Jesus Christ is ‘the Word’) by the Spirit of God. The only reason why we can have victory is because God is the one who fights our battles.
2 Corinthians 12:9 "And he said unto me, My grace is sufficient for thee: for my strength is made perfect in weakness. Most gladly therefore will I rather glory in my infirmities, that the power of Christ may rest upon me."
God's strength is made perfect in weakness, and he fought and won the battles even in our infirmities. To me, that is the most amazing part. That is the power of Christ that rest upon every truly born again believer by the grace of our God.
Ephesians 2:8-9 "For by grace are ye saved through faith; and that not of yourselves: it is the gift of God: Not of works, lest any man should boast."
The battle is fought in the heart, and the key to winning the fight is to trust in the LORD with all our hearts. It is through faith in every word of God in the 66 books of the Holy Bible that we are saved, not by our works.
Zechariah 4:6 "Then he answered and spake unto me, saying, This is the word of the LORD unto Zerubbabel, saying, Not by might, nor by power, but by my spirit, saith the LORD of hosts."
The LORD of hosts is our Redeemer, and he is strong (Jeremiah 50:34). For though we walk in the flesh, we do not war after the flesh: for the weapons of our warfare are not carnal, but mighty through God to the pulling down of strong holds, casting down imaginations, and every high thing that exalteth itself against the knowledge of God, and bringing into captivity every thought to the obedience of Christ (2 Corinthians 10:4-5).