The idea that only what is proscribed in Scripture is permissible is an idea known as the Regulative Principle. In the Reformed tradition of Protestantism the idea of the Regulative Principle has been a cornerstone for how the Reformed have tended to operate. It's why, as an example, in many historically Reformed churches hymns were not sung, but instead only the psalms were permitted. Not all Reformed churches, or all groups whose pedigree goes back to the Reformed tradition (which is most of Protestantism) follows the Regulative Principle in the same ways, or in an always consistent manner.
But the principle of "Where does the Bible say X?" as a per-requisite for something to be permissible is, in essence, the Regulative Principle in action. It is a unique feature of the Reformed Tradition to want explicit biblical proscriptions in order for something to be permissible.
Not all Protestants, let alone all Christians, follow the Regulative Principle.
Lutherans, for example, do not have the Regulative Principle. We have what is known as the Normative Principle, which rather than requiring Scripture to proscribe something in order for it to be permissible, we instead ask "Does Scripture forbid X?" What Scripture forbids is not permissible.
Under the Normative Principle there are three categories of things:
What Scripture commands, which must be done.
What Scripture forbids, which must never be done.
What Scripture neither commands nor forbids, which is adiaphora.
The word adiaphora is Greek (singular adiaphoron), and literally means "thing of indifference".
Scripture does not command that we have pews in our churches, Scripture does not forbid that we have pews in our churches; so can we have pews in our churches? It doesn't matter one way or the other, so it's okay to have pews, but it would be totally okay to not have pews as well.
Under the Normative Principle we have to look at things in a more nuanced way to decide if something is good and beneficial, or bad and harmful; if something is not forbidden, but not commanded, that does not necessarily make it okay, in the same way that it doesn't make something not okay.
That means we have to ask: Does this thing encourage faith in Christ? Does it edify and build up the Church? Does it point us to Jesus, does it provide a net good in the hearing of God's Word and the celebration of His Holy Sacraments? Does this thing harm the preaching of the Gospel, does it encourage and strengthen the preaching of the Gospel, does it do nothing either way?
So when the Lutheran Confessions caution against the Invocation of the Saints, it does not do so by using the Regulative Principle, but the Normative Principle; and it looks at the matter by asking, "Does this practice lead us to Jesus? Does it encourage and strengthen faith in the Gospel?" And the Lutheran Confessions come down negatively, looking at the ways in which Invocation of the Saints has been abused, and how the Faithful have, rather than benefited by the practice, been harmed by the practice.
Scripture does not command us to ask the Saints for their prayers; neither does Scripture forbid it. So the question of whether the Bible commands or forbids the practice is that Scripture does neither. So the follow-up question is: If we encourage the Faithful to invoke and seek out the saints in heaven for their prayers, is this practice something that benefits, encourages, strengthens faith in Christ? In the context of the practices and experiences of Christian life in the 16th century, the Lutheran Confessions conclude that it doesn't, and that it probably shouldn't be done. The position is not a particularly hard-line one, but rather it takes on a pastoral character counseling against it because there are certain unanswerable questions concerning it (e.g. we can't even know whether or not the saints in heaven can hear us, let alone respond), and abuses and abusive practice which can lead one to turn to the invocation of the saints rather than trust in Christ would be a detriment to faith, rather than a boon to faith. The practice, in and of itself, isn't forbidden in Scripture--but the Lutheran tradition has argued that asking the departed saints to pray for us is probably not worth the effort.
On the other hand, the Lutheran tradition has always maintained that the saints in heaven, and holy angels, do in fact pray for us. They pray for us even without our having to ask them to. This is because we actually see, in Scripture, the citizens of heaven praying for us, such as the angel who prays for God's people in the book of the Prophet Zechariah, or as we see those in heaven praying for those on earth in the book of St. John's Apocalypse. So the saints and angels do indeed pray for us here on earth. That's not in doubt, but the practice of seeking out their prayers by invoking them in our prayers is seen as, at best, probably unfruitful and at worse could lead us away from good and healthy faith in Christ.
To that end, while I do not ask the Blessed Virgin mother of our Lord Jesus Christ to pray for me, I do believe that she--and all God's precious saints above--do indeed pray for me as they pray for all of us. For in the Communion of Saints, both in heaven and one earth, God's People are united together in our Savior in faith, hope, and love. Our unity is found in Christ, by the power of the Holy Spirit, under the Fatherhood of God who is bringing all things toward His good purposes in Christ our Lord.
-CryptoLutheran
