1. Mary and Saint “Veneration”
Challies fails to define “To venerate” after stating it is nuanced. It does not mean “idol worship” as he seems to presuppose, rather, a Google search would have aided him in finding the definition, “great respect; reverence”.
How is this different than having “great respect” for Great grandfather Arthur, who served in WWII. As his descendants we desire to emulate the virtue of his courage, valor, loyalty, and sacrifice displayed in a time of great hardship. We do not bow down to him in adoration nor do we offer sacrifice to him as a deity, yet, we do revere him and desire to model the virtue he embodied. This veneration does not diminish the respect we have for his fellow soldiers or superiors; rather, it demonstrates their excellent qualities as well. In a greater way than we ever could, Jesus, being perfect, obeyed the Ten Commandments to their fullness; thus, honoring His mother Mary. No Catholic venerates Mother Mary more than her Son, Jesus.
Catholics do not “pray to” (in the way Protestantism understands) the Holy Ones (saints), rather, we “humbly request” (definition of “to pray”) them to intercede for us. This is no different than asking a spouse, friend, brother, or mother to intercede for you. It does not differ because we have Eternal Life. To disagree is to side with the Sadducees; do we not serve the God of the living and not the dead? Our communion with them is not lessened when they enter into the fullness of life. They remain, in a greater way, part of the Vine. How dare we to cut them off simply because we cannot see them. Jesus, who is fully human, communed with the “saints,” Moses and Elijah at the Transfiguration. If Catholics are guilty of “saint worship,” than the conclusive extension of said logic applies to Jesus.
In the same way, a person in Protestantism asks someone, who they readily identify with, to intercede for them, so do the faithful of the Church ask those Saints to intercede for us (cf. Hebrews 12:1 and 1 Tim. 2:1-3). We have great confidence in this because no unholy person may stand before the face of God (cf. Rev 21:27), and the prayers of the righteous availeth much (cf. James 5:16). Just as the Mother of God interceded on behalf of the people at the Wedding Feast of Cana (cf. John 2:1-4), so do we now recognize she intercedes for us at the Eternal Wedding Feast of the Lamb, along with all the other saints below the Altar (cf. 6:9-11). And she is always pointing toward her Son saying, “Do whatever He tells you” (cf. John 2:5).
The piece fails to adequately understand “worship”. The term is used by The Church in an ancient sense and was not simply developed 180 years ago in the United States with the advent of Fundamentalism. “…In common speech worship means adoration given to God alone. In this sense Catholics do not worship Mary or any of the other saints. But in older usage the term worship means not just adoration of God but the honor given to anyone deserving. It comes from the Old English weorthcipe, which means the condition of being worthy of honor, respect, or dignity. To worship in the older, larger sense is to ascribe honor, worth, or excellence to someone, whether a sage, a magistrate, or God. But there are different kinds of worship as there are different kinds of honor. The highest honor, and thus the highest worship, is given to God alone [sacrifice], while the honor or worship given to living men or to saints in heaven is of a different sort. Idolatry thus does not simply mean giving worship (in the old sense) to living men or to saints; it means giving them the kind reserved for God. …Consider how honor is given. We regularly give it to public officials. In the U.S. it is customary to address a judge as ‘Your Honor’. (It has been the British custom to address certain magistrates… as ‘Your Worship’…)”. 
The Jews believe in intercession of the saints as well, if only partially. They believe the “Archangel Michael protects and prays for the people of Israel (Dn. 10:21, 12:1).” And, “In the second century before Christ, the deceased High Priest Onias was seen praying for ‘the whole body of the Jews with outstretched hands’ (2 Mac 12:15).” Furthermore, and quite astonishingly for those in Protestantism, “For centuries, Jews have made pilgrimages to the Tomb of Rachel, considered the third holiest shrine of Judaism. Faithful Jews… praying… knowing that God will answer prayers through the intercession of Mother Rachel”  because she is “weeping for her children” (Jer 31:15).
To maintain consistency, Challies should no longer pray for anyone or ask anyone to intercede for him. Of course, that would be absurd, but consistent.
If Challies would have read the catechism for himself he would have read, CCC 2113:
“Idolatry not only refers to false pagan worship. Idolatry consists in divinizing what is not God. Man commits idolatry whenever he honors and reveres a creature in place of God, whether this be gods or demons (for example, satanism), power, pleasure, race, ancestors, the state, money, etc.”
Here is a link to understand The Intercession of the Saints. It is a biblical and historical understanding. Quotes from the earliest Christians attest to the validity of interceding/praying for one another.
St. Augustine of Hippo said,
“A Christian people celebrates together in religious solemnity the memorials of the martyrs, both to encourage their being imitated and so that it can share in their merits and be aided by their prayers” (Against Faustus the Manichean [A.D. 400]).
A Note: This is also discussed in this post: Wait, What?!? You DO Worship Mary!?!