Paul wrote to the saints at Philippi: "Be careful (worried) for nothing; but in every thing by prayer and supplication with thanksgiving let your requests be made known unto God. And the peace of God, which passeth all understanding, shall keep your hearts and minds through Christ Jesus. Finally, brethren, whatsoever things are true, whatsoever things are honest, whatsoever things are just, whatsoever things are pure, whatsoever things are lovely, whatsoever things are of good report; if there be any virtue, and if there be any praise, think on these things. Those things, which ye have both learned, and received, and heard, and seen in me, do: and the God of peace shall be with you." (Philippians 4:6-9, KJV)
Likewise, he wrote to the Christians of Colosse: "Put on therefore, as the elect of God, holy and beloved, bowels of mercies, kindness, humbleness of mind, meekness, longsuffering; forbearing one another, and forgiving one another, if any man have a quarrel against any: even as Christ forgave you, so also do ye. And above all these things put on charity (love), which is the bond of perfectness. And let the peace of God rule in your hearts, to the which also ye are called in one body; and be ye thankful." (Colossians 3:12-15, KJV)
As the context of these two verses clearly demonstrates, the meaning of the Greek word translated into English as "peace" denotes a state of tranquility and felicity. Paul says this kind of peace is beyond the ability of our intellects to quantify or define. Hence, it is not an understanding - it is a state of mind.
Even so, Paul clearly indicates that the way for Christians to achieve this peace is to let go of burdens and not worry over things. This is consistent with what Jesus Christ had told his disciples during his earthly ministry. After telling them that it was impossible to serve two masters, he said: "That is why I tell you not to worry about everyday life - whether you have enough food and drink, or enough clothes to wear. Isn't life more than food, and your body more than clothing?...Can all your worries add a single moment to your life?...So don't worry about these things...These things dominate the thoughts of unbelievers, but your heavenly Father already knows all your needs." (Matthew 6:25-32, NLT)
God's peace is a special blessing that is available to Christians, but we have to be willing to let go of our anger, hurts, worries and concerns to receive it. Maybe that's why one of Paul's favorite greetings and salutations was, "Grace be unto you, and peace, from God our Father, and from the Lord Jesus Christ." Brethren, God wants us to have that peace; but we have to let go and allow it to wash over us.