16 We have come to know and have believed the love which God has for us. God is love, and the one who abides in love abides in God, and God abides in him.
17 By this, love is perfected with us, so that we may have confidence in the day of judgment; because as He is, so also are we in this world.
I've met many Christians who have agreed strongly and quickly with the truth that God loves them. But, you know, very few of them actually believed it. It was possible to tell that this was so because they operated from a motive of fear much of the time in their walk with God. This fear manifested in various ways: Anxiety over the genuineness of their salvation, fear of the hurtful wrath of God in response to their sin, even a belief that their salvation would be withdrawn by God if they didn't step just right. This fear produced a moralistic preoccupation with obedience to God's commands which, in turn, engendered a legalistic character of living. But such legalism always births hypocrisy, and spiritual exhaustion, and deep unhappiness within the Christian believer. It also creates in them a sourness toward other believers - especially those who are not likewise fearful, legalistic and mired in hypocrisy.
It's a dangerous thing, then, merely to know about God's love, to assent intellectually to it, but not to be thoroughly convinced of it. The apostle John made this distinction in the passage above: "We have come to know and have believed the love which God has for us." (vs. 16) Knowledge is a predicate of belief, but it isn't synonymous with belief; one can know a thing but not truly believe it. The apostle James wrote on this head in his epistle in the New Testament:
James 2:18-20
18 But someone may well say, "You have faith and I have works; show me your faith without the works, and I will show you my faith by my works."
19 You believe that God is one. You do well; the demons also believe, and shudder.
20 But are you willing to recognize, you foolish fellow, that faith without works is useless?
True belief, saving belief, life-transforming belief always inevitably (though, not necessarily) results in corresponding action. This is what distinguishes such belief from mere intellectual assent. Demons believe that there is one God, but there is no positive reflection of that belief in their conduct in the slightest. In the same way, many Christians believe God loves them but there isn't the slightest positive reflection of that belief in their living.
Such true belief, the apostle John wrote, is reflected in "confidence (or "boldness," in the KJV) in the Day of Judgment." (vs. 17) Rather than a "fearful looking for of judgment and fiery indignation" (Hebrews 10:27), the believer who has believed the love God has for them, gains boldness with God, a confidence before Him that they stand, not under His wrathful judgment, but in God Himself, who is Love (vs. 16). The effect of this firm conviction of the divine love wherein they stand dissolves fear and its exhausting, terrible torment.
So, how about you? Is a craven fear of God's wrath motivating your walk with Him? Are you a frightened inmate in the prison of God's dreadful, punishing power? Or a joyful "joint-heir with Christ" (Romans 8:17) in the kingdom of God's love? Do you know AND BELIEVE the endless, perfect love God has for you? When you do, you'll know it because fear will be cast out and you will come "boldly before the throne of grace," in joy and peace, as God's dearly beloved child.