The 6th article of the Anglican Thirty-Nine Articles of Religion reads, in part, as follows:
Of the Sufficiency of the Holy Scriptures for Salvation.
Holy Scripture containeth all things necessary to salvation: so that whatsoever is not read therein, nor may be proved thereby, is not to be required of any man, that it should be believed as an article of the Faith, or be thought requisite or necessary to salvation. In the name of the Holy Scripture we do understand those canonical Books of the Old and New Testament, of whose authority was never any doubt in the Church.
Holy Scripture containeth all things necessary to salvation: so that whatsoever is not read therein, nor may be proved thereby, is not to be required of any man, that it should be believed as an article of the Faith, or be thought requisite or necessary to salvation. In the name of the Holy Scripture we do understand those canonical Books of the Old and New Testament, of whose authority was never any doubt in the Church.
Such sentiment reflects much of modern Protestant (both Anglican and non-Anglican) thought about the “sufficiency” of the Bible on the topic of the (eschatological) salvation of a believer. Firstly, it should be noted that Protestants often confuse “material” and “formal” sufficiency with one another and such is reflected in this statement; furthermore, another major problem with the common claim that the Bible contains all things necessary for salvation is that such a working definition of the doctrine of sola scriptura is that, like the difference between Newtonian physics and quantum physics. The Bible (and other Scripture, too) can perhaps be considered a sufficient guide only until you reach the level of life where Scripture does not penetrate. With respect to the Anglican Articles of Religion, such were composed in the 16th century, long before people could understand and define the precise biological processes occurring in the conception and gestation of the human baby in the female uterus. It was often just assumed that the womb was sacred and should not be violated. However, in modern times, men have seen the gestation process under a microscope, assigning terms to the primitive stages and development such as zygote, blastula, embryo, and foetus, resulting in debates both in and out of religious circles as to when such should be considered a human person and mere “undeveloped tissue.” An appeal to the Bible is limited in answering this (literally) life-or-death question, for while the Bible alludes to life in the womb (e.g., Exo 21:22-24; Psa 139:13-16; Luke 1:39-45), it does not define when human life begins or does it give any information on the reasons life could be artificially aborted in-utero. One could claim then, using the premise given in the Thirty-Nine Articles, that since the Bible does not forbid aborting a blastula, it is perfectly alright to do so. Of course, within Protestantism, there are a plethora of various views on the topic of if/when abortion is permissible. There are many other areas where Christians need an external authority and God-glorifying answers. For example, note the following issues that have much contemporary currency but the Bible either does not address these issues or to those that it does address, the answer is often unclear: contraception, artificial insemination, test-tube fertilisation, genetic engineering, surrogate motherhood, sterilisation, masturbation, sex education, eugenics, cloning, equal rights for women, capitalism and the use of wealth, the use of alcohol and mind-altering drugs, usury, cremation, psychology, resistance to tyranny, labour strikes, when it is permissible to go to war in the New Covenant (cf. "just war theory"), slavery, church/state relations, etc. All of these are part of a believer's "spiritual life."
This definition of “sola scriptura” and the comments about the contents of the Bible is false. Furthermore, it shows that we need a source external to Scripture (not just the Bible) that can, when lead by the Holy Spirit, give us authoritative answers on these and other moral and theological issues if/when they arise. On issues such as abortion where a human life hangs in the balance, one’s best guess is not enough.