The Lord's Prayer is not simply a template to teach us how to pray, but rather it is a prayer itself. Jesus taught his disciples and us to pray. The content of the prayers is not based on the number of words but rather it is the truthfulness and openness of a heart that counts. In prayer we don't need a long list, asking for many things but focussing upon what are essential for our internal peace and ask God to strengthen our faith in Jesus.
Our Father who art in heaven: In prayer Jesus taught the apostles to give thanks to God who is Father of all. We are God's children by adoption (Eph 1,5) and as a children of God we are heir of the kingdom. It is our final goal, our final destination. We give thanks to God for adopting us to be children of God. Our prayer is able to reach heaven because God wants it to - we are on earth but talk to God who is in heaven. As children of God we need to make our Father known to all creation and that is God's will.
Your kingdom come: It is the teaching of John the Baptist and the teaching of Jesus and of the apostles after they witnessed the Lord's Ascension. God's kingdom come is not only the prediction that God has won the final victory but it is the assurances that God's glory will be prevailed to all the nations. The prediction is fulfilled in Jesus on his resurrection and Ascension; the former claims the final victory and the latter is the completion of His mission on earth.
God's will be done on earth as it is in heaven. Jesus came to this world to make known God's will for us and He alone knows God's will because He came from God. He alone fulfilled God's will on earth. Jesus made this public confession on the Garden when He prayed: if it is possible take this cup away from me but not mine, your will be done (Mat 26,38)
Give us this day our daily bread: It is the reminder of God's care and love for our ancestors who journeyed toward the Promised Land, they daily collected manna for food. It is the same care and love God gives to those who place their trust in God and receive abundant God's grace for their spiritual journey. The physical and spiritual needs of each individual reflect the need of a wider community. It is our duty towards God and towards our neighbours to care for others both physical and spiritual needs. We ask for daily bread because we trust in God's fatherly love and care.
Forgive us our trespass it: We pray not to follow our own will because it often leads to selfishness. Selfish is a form of sin. Not wanting to change our bad habits is a form of temptation. We pray not to fall into that trap and pray to have the courage to forgive as we have received forgiveness from God.