Q: What doth the preface of the Lord's prayer teach us?
A: The preface of the Lord's prayer which is, Our Father which art in heaven, teacheth us to draw near to God with all holy reverence and confidence, as children to a father, able and ready to help us; and that we should pray with and for others.

Isaiah 64:9. Be not wroth very sore, O Lord, neither remember iniquity for ever: behold, see, we beseech thee, we are all thy people.
Luke 11:13. If ye then, being evil, know how to give good gifts unto your children: how much more shall your heavenly Father give the Holy Spirit to them that ask him?
Romans 8:15. 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.
Ephesians 6:18. Praying always with all prayer and supplication in the Spirit, and watching thereunto with all perseverance and supplication for all saints.
Acts 12:5. Peter therefore was kept in prison: but prayer was made without ceasing of the church unto God for him.
Zechariah 8:21. And the inhabitants of one city shall go to another, saying, Let us go speedily to pray before the Lord, and to seek the Lord of hosts: I will go also.

Westminster Project - See John Flavel's exposition of the WSC for more thoughtfulness on question 100