The Westminster creed is based mostly on the Westminster Shorter Catechism, it is taken from the Pastor’s Book p329/330 (Kent Hughes & Douglas Sean O Donnell, Crossway) but no source is given for it…
I believe man’s chief end is to glorify God, and to enjoy him forever.
I believe that the word of God, contained in the Scriptures of the Old and New Testaments, is the only rule given to direct us how to glorify and enjoy God.
I believe God is a spirit, infinite, eternal, and unchangeable in his being, wisdom, power, holiness, justice, goodness, and truth; I believe there is but one true living God; that there are three persons in the Godhead: the Father, the Son, and the Holy Ghost; and that these three are one God, the same in substance, equal in power and glory; I believe God has foreordained whatever comes to pass; that God made all things of nothing, by the word of His power, in the space of six days, and all very good; and that God preserves and governs all His creatures and all their actions.
I believe our first parents, though created in knowledge, righteousness, and holiness, sinned against God, by eating the forbidden fruit; and that their fall brought mankind into an estate of sin and misery; I believe God determined, out of His mere good pleasure, to deliver His elect out of the estate of sin and misery, and to bring them into an estate of salvation by a Redeemer; I believe the only Redeemer of God’s elect is the Lord Jesus Christ, who, being the eternal Son of God, became man, and so was, and continues to be, God and man in two distinct natures, and one person, forever; I believe Christ, as our Redeemer, executes the office of a prophet, of a priest, and of a king; I believe Christ as our Redeemer underwent the miseries of this life, the wrath of God, the cursed death of the cross, and burial; He rose again from the dead on the third day, ascended up into heaven, sits at the right hand of God, the Father, and is coming to judge the world at the last day.
I believe we are made partakers of the redemption purchased by Christ, by the effectual application of it to us by his Holy Spirit; I believe God requires of us faith in Jesus Christ, and repentance unto life to escape the wrath and curse of God due to us for sin; I believe by His free grace we are effectually called, justified, and sanctified, and gathered into the visible church, out of which there is no ordinary possibility of salvation; I believe that we also are given in this life such accompanying benefits as assurance of God’s love, peace of conscience, joy in the Holy Ghost, increase of grace, and perseverance therein to the end; that at death, we are made perfect in holiness, and immediately pass into glory; and our bodies, being still united in Christ, rest in their graves, till the resurrection; and at the resurrection, we shall be raised up in glory, we shall openly be acknowledged and acquitted in the day of judgement, and made perfectly blessed in the full enjoying of God to all eternity.
(Emphasis in original.)