Simplistic Paraphrasing of the Summa Theologica

Summa Theologica 

from the New Advent website

Introduction

Because the doctor of Catholic truth ought not only to teach the proficient, but also to instruct beginners 

St. Thomas intended his Summa (i.e. summary) of theological thought for the teacher as well as the beginner.

(according to the Apostle: As unto little ones in Christ, I gave you milk to drink, not meat -- 1 Corinthians 3:1-2),

In this verse from 1 Corinthians, St. Paul is admonishing the Corinthians because they have not advanced in the knowledge of Christ. 

we

I don't know who he means by "we".  Perhaps he is using it in the sense of the Royal "we", wherein, those in authority represent all in authority and those who have gone before and perhaps even that they speak as representatives of God.

purpose in this book to treat of whatever belongs to the Christian religion,

The Summa, then, is about teaching the Christian faith.  Not any other.

in such a way as may tend to the instruction of beginners.

And, it is intended to simplify the matter in order that beginners may better understand it.

We have considered that students in this doctrine have not seldom (not seldom i.e. frequently) been hampered by what they have found written by other authors,

St. Thomas feels that most teachers of theology, in his day, were boring.  Therefore, students who wanted to learn theology, stopped, because the authors bored them with ...

partly on account of the multiplication of useless questions, articles, and arguments,

...silly questions,...

 partly also because those things that are needful for them to know are not taught according to the order of the subject matter, but according as the plan of the book might require, or the occasion of the argument offer,

 ...illogical organization of the material,...

 partly, too, because frequent repetition brought weariness and confusion to the minds of readers.

...and, too much repetition.  All these things confused the students and they dropped the subject.

Endeavouring to avoid these and other like faults, we shall try, by God's help, to set forth whatever is included in this sacred doctrine as briefly and clearly as the matter itself may allow.

So, St. Thomas seeks to correct these faults.  His intention is to be very brief and quite clear in his teaching of the Christian faith.

The following is the outline of his book, the Summa Theologica.  The links will take you to the New Advent website.

PRIMA PARS.
Sacred Doctrine. The One God. The Blessed Trinity. Creation. The Angels. The Six Days. Man. The Government of Creatures.

PRIMA SECUNDÆ PARTIS.
Man's Last End. Human Acts. Passions. Habits. Vice and Sin. Law. Grace.

SECUNDA SECUNDÆ PARTIS.
Faith. Hope. Charity. Prudence. Justice. Fortitude. Temperance. Acts Which Pertain to Certain Men.

TERTIA PARS.
The Incarnation. The Life of Christ. Sacraments. Baptism. Confirmation. The Holy Eucharist. Penance.

SUPPLEMENTUM TERTIÆ PARTIS.

Penance (continued). Extreme Unction. Holy Orders. Matrimony. The Resurrection. Appendices.