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."
The word "waxed" means "to become gradually more intense or to increase" and shows that this condition of the heart is not something we are born with or that strikes us suddenly. It has to be nurtured over a prolonged period of time. This is why we should not violate our conscience, even in small things. Guarding our conscience will keep us sensitive to God and will stop our hearts from becoming hardened. If we will stay faithful to God, even in the small things, then we will be faithful in the more important things also.
Keeping the commandments doesn't affect God's willingness to love us, but it affects our awareness of how much He loves us. If we live in sin, our conscience becomes defiled and it condemns us. It's not God condemning us, but our conscience. God still loves us. John was speaking of this same thing in 1 John 3:20, when he said, "For if our heart condemn us, God is greater than our heart, and knoweth all things." However, as far as this earthly life goes, our awareness of God's love is everything. Therefore, we must keep Satan from blinding us to the love of God.
The most effective way of doing this is to give no place to the devil through sin. John went on to say in 1 John 3:21, "Beloved, if our heart condemn us not, then have we confidence toward God." Holiness is essential in keeping our hearts assured of the love of God (1 John 3:19). It's the nature of a Christian to walk in the light and not in darkness. When you are rightly informed of who you are and what you have in Christ, holiness just naturally flows out of you. That's your nature.